re: Slab leak detection - plumber recommendation?

The plumber who actually found the leak and rerouted assured me that he could do more with a stethoscope than LD could with their gadgets. A neighbor of mine has been chasing a damp slab at a corner of the house for years. There's so little rain now that he has no problem, but he added regular drains at downspouts a few months back. Fortunately, he has a ditch to drain into.