Definately feel for you. It's always hard to deal with losing your plants. Hope they crashed their dirt bikes and somehow your babies impaled their asses.
It's a hassle, but it's smart to invest in tall plants to go around them and maybe even a fence.
I've heard of people using sheets of metal to make power boxes and put signs on fences (like will prosecute if trespass or something).
One of the big problems when growing outside, is you're usually on someone elses property. They may have been ripped out by a property owner who doesn't want to get busted. That's the chance you take.
And how well did you hide them? If they were able to ride the bikes right up to your plants, they weren't very stealth.
Most people I know, that grow outdoors, have a one or two hour walk just to get to them.
Hate to be a downer, just something to think about.