Unfortunately, unless you can watch him 24/7 he will get on the counter if he wants to. You can buy those little spritzers that go off every few minutes, which might detour him, but if he is a curious kitty, that might end up on the floor, too. We have been very lenient about letting the kits on the counters, so I am not much help...
The only advice I can give you is to make sure the counters aren't appealing to him. Don't leave anything that looks like it could be fun on there.
We had a brand new loaf of bread on the counter and I woke up the next morning and Ziggy had eaten a hole right through the bag and into the bread. We put our bread in the cupboard now, and I try to keep as much stuff as possible off.
Every once in a while I will spray them if they are messing with stuff, but you are really fighting a losing battle here.