Block back-end completely !

This is the most annoying thing in wordpress..

How do we block all the bunch of /wp-admin/ + /wp-login urls and functions for low level users, I really do mean COMPLETELY ?!

I’m using frontend register, edit profiles, lost password plugins.. but one way or another anyone can still access /wp-admin/ + /wp-login/.

I hope there are some experts out here that can help. Fed up with using 10 different plugins and still not being able to solve this, its driving me mad!