It is not just the water mains that you might encounter when lowering a patio. At the rear of our house all of the drainage and sewage pipes are so close to the surface that they prevent the patio from being lowered any further. As such the damp proof course for the house is only ~ 1.5 bricks above the patio as opposed to the standard of at least 2 bricks. It is a pre-war semi which I suspect was built like this as there is no evidence of the house ever subsiding. Given that utility pipes and cables are not always installed to regulatory minimum depths I would be very wary of using a sledge hammer to break up any hard surface close to the house. Could well pay to hire or acquire a concrete breaker to hopefully avoid percussion damage to a buried pipe.
Ground penetrating radar came to mind regards pipe detection then my mind immediately wandered off to The Falkland Islands. I know that the
argies dumped a huge amount of mines there in areas which were fenced off in 1983 and left uncleared as it was felt that the risks in clearing them were not worth the benefit. Plastic mines were a particular problem re detecting them and the technology available then was not ... Actually I think that I'd better stop before someone asks for the thread to be closed. Lol.
