Prevent colliders from climb other colliders

hey!

In the game im making the characters use box colliders because they are tanks and capsule style colliders didnt work really well, well I have this problem were if you walk against a wall you can actually climb the wall I want to prevent my character from doing that. The walls are also box colliders but this happens with terrain as well even on 90º cliffs if you walk against it eventually you can climb it, I want to prevent my player from leaving the arena

 

I posted something similar earlier, maybe this could help you:

http://forum.unity3d.com/threads/character-movement-and-slopes.290381/