This is something I can't stress enough, and I'm sure I have a lot to back it up. DO NOT USE HARMFUL/LETHAL DEVICES TO SECURE YOUR PLOT! "These marijuana growers use bear traps, sawed off shotguns with tripwires, etc. to protect their crop" That looks bad on the cannabis community. Avoid it. There's something called camouflage. Use the native brush to your advantage. I'm aware that cannabis doesn't blend into the vast majority of forests. Sh*t happens.
I've heard of people using infrared systems to take pictures and record videos when something specific enters the area. Though it won't stop theft, it can be useful for spotting law enforcement so you can stay away. Alarms that are connected to tripwires can also draw attention – but if you make them subtle enough, they'll just scare away the intruder. So remember: use your imagination and remain safe.