electric fence idea is out. just realized that all they need to do is come back with some rubber handled snippers.
new idea: slats. buy about 100-150 2''x2''x8's and put them every six inches or so. that way they'll need to come back with a saw if they want to get in and saw away at wood for a good 10 minutes.
the beauty of this plan is that i can affix the plastic to the slats, thereby making it less likely to move and set off false positive on the motion sensors.
i still want to put an electric fence behind the slats though. just for good measure.