1)
http://forums.polserver.com/ftopic1924.php
2) Multis are set of items (defined at client side) that can be created from server side. Player bought houses and boats are multis. And the statics, all unmovable items in world map (towns, bridges) are defined in statics.
3) The part you want to destroy, must be either a multi or dynamic items. There's also dynamic multis (the correct way to handle this), but since POL core doesn't support them, it's a lot and lot of work to use. Easiest way is to create the wall from dynamic items and make a script to delete/modify those items with text-command or what ever you want the trigger to be. The downside in that method is increase in network latency, when server has to send the items every time player goes near the wall. Modifying and using multi files gives a solution to this problem, but in this case, players must download the new multi files every time the files are modified (ie. you want to add a new type of breakable wall.)
