Blood meal and urea will keep the plant eaters away, you're just going to have to rely on a secluded spot to keep it hidden from the prying eyes of other people. Don't set "traps" that will hurt a person unless you fancy getting ass raped for the next 10-20 years..
Hey, my dad used this alot and it worked all the time....It will protect if you have a big crop....Most people see a plant or a few and wait to steal them. Normally they come back at night and yank the shit from the ground and run. He put razor blades around the base stem of the plant...just a little tape and some blades...or tie them to string anything like that. One guy tried to steal his crop one time grabbed the first one and tore his shit all up...He woke up the next morning one was gone, blood everywhere but the other 4 were still standing....other than that not much else you can do if someone really wants to jack your shit...good luck
Fishing line to stop deer? I don't think so. I suppose it could work, on a really sick, puny deer, but doubt it. Deer can launch themselves 6-10' feet in the air from standing still and land three feet away, just beyond almost any fence. If they get a hankerin' for your weed, it's pretty much gone.