Game camera at the gates they have to use to get in would be great. No flash, hidden is key. You can catch them coming & going. Of course at this point they've probably taken all they wanted.
I agree, property theft is a big tick-me-off thing.
Who would know what was back there? I know of a fellow who baled people's hay. All too often after he worked a field, any 'valuables' from that field disappeared (equipment, deer feeders, etc). If it is visible from the road, well that's the problem.
The real problem is that crime does pay. There are zero to little consequences in the rare chance they actually are caught. And it's easier than getting a job. If only more thieves were executed in the act, many others would decide the theft career is too difficult. But until then...