Kayıt içerisinde tekil id için kullanılan guid in uzun olduğunu düşünüyorsanız, onun yerine aşağıdaki fonksiyonu kullanın, ama üretilen sayı/harf silsilesi ne kadar uzun olsada çok düşük ihtimallede olsa tekil olmayacaktır, o yüzden yinede kayıt sırasında kontrol edilmesi gerekir. Alıntı yaptığım sayfa bitly yada goo.gl gibi kısaltma url projesi için hazırlanmış.

        private static string shorturl_chars_lcase = "abcdefgijkmnopqrstwxyz";
        private static string shorturl_chars_ucase = "ABCDEFGHJKLMNPQRSTWXYZ";
        private static string shorturl_chars_numeric = "23456789";

        public static string RandomCharacters(int feedCount)//feedCount burada tekil kodun uzunluğu
        {
            // Create a local array containing supported short-url characters
            // grouped by types.
            char[][] charGroups = new char[][] 
            {
                shorturl_chars_lcase.ToCharArray(),
                shorturl_chars_ucase.ToCharArray(),
                shorturl_chars_numeric.ToCharArray()
            };

            // Use this array to track the number of unused characters in each
            // character group.
            int[] charsLeftInGroup = new int[charGroups.Length];

            // Initially, all characters in each group are not used.
            for (int i = 0; i < charsLeftInGroup.Length; i++)
                charsLeftInGroup[i] = charGroups[i].Length;

            // Use this array to track (iterate through) unused character groups.
            int[] leftGroupsOrder = new int[charGroups.Length];

            // Initially, all character groups are not used.
            for (int i = 0; i < leftGroupsOrder.Length; i++)
                leftGroupsOrder[i] = i;

            // Because we cannot use the default randomizer, which is based on the
            // current time (it will produce the same "random" number within a
            // second), we will use a random number generator to seed the
            // randomizer.

            // Use a 4-byte array to fill it with random bytes and convert it then
            // to an integer value.
            byte[] randomBytes = new byte[4];

            // Generate 4 random bytes.
            RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
            rng.GetBytes(randomBytes);

            // Convert 4 bytes into a 32-bit integer value.
            int seed = (randomBytes[0] & 0x7f) << 24 |
                        randomBytes[1] << 16 |
                        randomBytes[2] << 8 |
                        randomBytes[3];

            // Now, this is real randomization.
            Random random = new Random(seed);

            // This array will hold short-url characters.
            char[] short_url = null;

            // Allocate appropriate memory for the short-url.
            short_url = new char[random.Next(feedCount, feedCount)];

            // Index of the next character to be added to short-url.
            int nextCharIdx;

            // Index of the next character group to be processed.
            int nextGroupIdx;

            // Index which will be used to track not processed character groups.
            int nextLeftGroupsOrderIdx;

            // Index of the last non-processed character in a group.
            int lastCharIdx;

            // Index of the last non-processed group.
            int lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;

            // Generate short-url characters one at a time.
            for (int i = 0; i < short_url.Length; i++)
            {
                // If only one character group remained unprocessed, process it;
                // otherwise, pick a random character group from the unprocessed
                // group list. To allow a special character to appear in the
                // first position, increment the second parameter of the Next
                // function call by one, i.e. lastLeftGroupsOrderIdx + 1.
                if (lastLeftGroupsOrderIdx == 0)
                    nextLeftGroupsOrderIdx = 0;
                else
                    nextLeftGroupsOrderIdx = random.Next(0,
                                                         lastLeftGroupsOrderIdx);

                // Get the actual index of the character group, from which we will
                // pick the next character.
                nextGroupIdx = leftGroupsOrder[nextLeftGroupsOrderIdx];

                // Get the index of the last unprocessed characters in this group.
                lastCharIdx = charsLeftInGroup[nextGroupIdx] - 1;

                // If only one unprocessed character is left, pick it; otherwise,
                // get a random character from the unused character list.
                if (lastCharIdx == 0)
                    nextCharIdx = 0;
                else
                    nextCharIdx = random.Next(0, lastCharIdx + 1);

                // Add this character to the short-url.
                short_url[i] = charGroups[nextGroupIdx][nextCharIdx];

                // If we processed the last character in this group, start over.
                if (lastCharIdx == 0)
                    charsLeftInGroup[nextGroupIdx] =
                                              charGroups[nextGroupIdx].Length;
                // There are more unprocessed characters left.
                else
                {
                    // Swap processed character with the last unprocessed character
                    // so that we don't pick it until we process all characters in
                    // this group.
                    if (lastCharIdx != nextCharIdx)
                    {
                        char temp = charGroups[nextGroupIdx][lastCharIdx];
                        charGroups[nextGroupIdx][lastCharIdx] =
                                    charGroups[nextGroupIdx][nextCharIdx];
                        charGroups[nextGroupIdx][nextCharIdx] = temp;
                    }
                    // Decrement the number of unprocessed characters in
                    // this group.
                    charsLeftInGroup[nextGroupIdx]--;
                }

                // If we processed the last group, start all over.
                if (lastLeftGroupsOrderIdx == 0)
                    lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
                // There are more unprocessed groups left.
                else
                {
                    // Swap processed group with the last unprocessed group
                    // so that we don't pick it until we process all groups.
                    if (lastLeftGroupsOrderIdx != nextLeftGroupsOrderIdx)
                    {
                        int temp = leftGroupsOrder[lastLeftGroupsOrderIdx];
                        leftGroupsOrder[lastLeftGroupsOrderIdx] =
                                    leftGroupsOrder[nextLeftGroupsOrderIdx];
                        leftGroupsOrder[nextLeftGroupsOrderIdx] = temp;
                    }
                    // Decrement the number of unprocessed groups.
                    lastLeftGroupsOrderIdx--;
                }
            }

            // Convert password characters into a string and return the result.
            return new string(short_url);
        }

http://www.java-frameworks.com/csharp/shorturldotnet/ShortUrl.Utils.cs.html