just find anywhere where there are plenty of rocks and other stuff to turn over. Try along the wall edge behind the business park, loads of rocks there to flip - very sinky muddy ground though.
One thing though - unless you've asked the owners and got their permission, don't raid peoples tyre traps. The owners are very protective of their time and effort to lay them (understandably)... spoke to one guy last weekend who was going livid because someone had been digging up all the tyres he'd laid.