I was playing as my Wizard and I was up against a golem protecting some treasure. I was all alone in a small room, and to block the entrance and prevent the golem from getting to me, I used the power Witch Thorns:
Wall 3 within 10 squares, The wall creates a zone that lasts until the end of the encounter. The zone can be up to 4 squares high and must be on solid surface. The zone can provide partial cover and blocks line of sight. The zone is difficult terrain. and when any attempts to leave a square in the zone, the creature must succeed on a saving throw or be immobilized until the start of its next turn. Once per round as a minor action, you can expand or contract the zone by 2 squares in any direction.
I thought this basically sealed up the entrance and made sure the golem couldn't get to me or even see where I was, but the DM had the golem just charge through it. The DM said that its just normal difficult terrain and it can get through the wall.
I don't know the rules about walls, but I guessed that the reason for making walls is so that creatures have to climb over them or go around them to get to you. Is that true that enemies can go through your walls?