The best way is prevention. Let them on your server, let them hack, catch them in the act, and then ban their steamID so they wont ever come back. You dont even have to be there, look through your servers logs, you can generally tell. Such signs include
-Everyone yelling "leave you stupid hacker" or "voteban"
-One person has 100 kills, 0 deaths.
-Etc.
Then you can ban them. Also some sites have giant black/white lists of peoples steamID's who hack. Just copy it into your banned.cfg (or whatever its called).
Although if you must, VAC is the most security Ive ever needed. I also have mani mod, it has a built in hack banner system, but its nothing compared to VAC.
Dont worry so much about hackers, if its a good server and fun, no one will leave, and the hacker will get bored of hacking.