Here's the thing...Cops aren't going to do anything if it's just a couple of plants. Would you really want the cops to know you're growing? Even if you're completely legal. Assuming they actually care and find your plants, they're gonna be all fucked up anyway so you're still not going to get them back....In the end, what have you really gained? Other than cops knowing about you, nothing.
As for being there while it happens...Let's assume you're too scared to fight them or for whatever reason you don't confront the bastards...Why not make some noise? Yell, scream, cry...whatever...I have yet to hear of a situation where the robber continues robbing the house after someone walks in on them...just doesn't happen...first reaction is to haul ass out of there...