Sure, but that depends on your situation.
1. If your regular customers log on from the same networks consistently, filter unwanted login attempts with netfilter and/or tcp_wrappers. Problem solved.
2. If your regular customers log on from the same machines consistently, enable pubkey authentication and disable all other authentication. Problem solved.
I recommend #1 or #2, or both.
3. If you can't do #1 or #2, move sshd to listen on a different port (e.g. 123). This is a sucky security measure, though, and will only stop the script kiddies.
4. If you can't do #1, #2, or #3, then make sure your users have strong passwords. You can enforce this with John or some such.