I agree with 68RATVT on this one, find out who the owner is and ask permission first. Before anything. I live in a rural area, and if I see anyone sneaking around I investigate with a rifle in my hand.
There's some goodies in my sheds, they're mine and I intend to keep them.
When I told the local Plod what I do, I demonstrated with a imaginary rifle: "There will be a warning shot over their heads," (rifle paralel to the ground,) "Then one aimed at them." (rifle pointed sky-ward.)
The cop looked me in the eye and said: "So long as there's two shots."
Don't mess with someone elses property. You could live to regret it. Or you might not.