Honestly, you should ask you neighbor what he was doing. It's hard to believe they could generate a big enough field to do anything to your security system. It's also hard to figure out what they are trying to do. The only reason I can think of to run wires into a field is for a ham radio setup. A long antenna can boost your reception, but I don't think you would want to bury it.
Still, if you have wires on your property, you can just cut them. You don't have to dig them up.