Sorry to hear...
Something I used is a mixture of epoxy and milled fiberglass to pour/apply over the heads of fasteners especially key fasteners to discourage thieves... they likely will pass on trying to take anything that requires work/time...as aversion to work is the reason they are thieves in the first place... also grinding heads off some key fasteners works well too. And along that line of thought, yield to torque fasteners may also be used.