There are many solutions, most of which cost money. The sad and simple fact is that a thief will usually find a way regardless of most hurdles you put in their way. A total lack of respect for others property.

We have 6 larger sized ones at our field, and even though we have a locked gate, it would be very easy to take them. The wind usually takes care of one a year. Worst case, we would just do away with them and have folks bring there own. Some already do, they are easy to move around now, and pretty cheap at $50.00

Good luck either way.