My sympathies are with you also.
We regularly have break in's down at the lotties, 3 of the gardens so far this week have had sheds broken into!
Security is a major problem here no matter what time of year. We have security gates on every entry and the secretary of the allotments is often keeping watch over the place until after 2am!
Only a fortnight ago we caught 2 youths coming out of a plot (over the fence in daylight) who strolled off casually when asked what they were doing, and yesterday there was a gang of kids aged from 12 - 16ish wandering around where they shouldn't be.
It's a constant worry as our shed was broken into last year ( they stole a hammer and left my saddles for the horses!) and our old caravan was burnt to the ground last month (which had been previously broken into).
We do try to go there every day at varied times, but do sometimes think that it's pretty hopeless.
Not only do they break in and steal things they also damage property and our spirits. This week someone has also been into our almost finished polytunnel and ripped the plastic, we found rifle pellets inside next to the tear and can only assume they were trying to get the rabbits that are everywhere.
Irresponsible, disrespectful, thieving, lying B******s!!!
But as said in another post, there isn't even much that can be done if we catch them in the act!