You may want to give more details about what you're trying to accomplish, because...

[user@host]$ ll /bin/su
-rwsr-xr-x 1 root root 30148 Jul 21 19:54 /bin/su
[user@host]$ ln -s /bin/su notsu
[user@host]$ ./notsu
Password:
[root@host]#
[download]

So if you're trying to use this to prevent people from running su it's probably not a good idea.