@Ieuan It'd be better to do it on the server, or you don't uncover bugs due to the player doing something with something being different than the player that actually placed the block
That was a resounding theme in the 1.7.2 pack I put together that we played a while back. Telepads and AE2 in particular were problematic, didn't know it because I tested it entirely in single player
I have a mob farm that works pretty good, it's basically the one pahimar always builds (water to send them down a pit where they die combined with slabs to prevent spiders) except mine is modular
The bottom has water and 9 iron spikes to kill the zombies via spikes and not have to worry about fall damage