I think it would cause to much balancing problems tho i dont like that idea much =P and for some "unique" traps it is hard to mod. And bdw aametherar that wall trap... wouldnt be walls visible allreay ?=) and you need time to build such a trap.... enemy can just go different way and you were building it for 5 days for nothing ?=) you cant just pop it in within 1 sec as fight goes. You need to be 100% sure about time and location of an attack to start build ther but that is almost imposible and just nubs would go into it.... without seeing/realizing it (wow trolls at wheels and ohoh hidden wall in grass =)) or did i missed something ?=P
Picture made by Aametherar the orc
Glory to the elves!