Re: Lawn sprinklers
It should be fairly obvious by where the sprinklers are located both their physical location in the ground as well as their proximity to the control valve, though this is not always the case, particularly if there are flower bed drip systems as well.
Probably the easiest thing is to douse for them. Get yourself a wire coat hanger and cut the lower cross bar and one arm out of it. The section you remove should then be straightened slightly to a right angle. You loosely hold the short leg in your fist so that it can freely swivel while simultaneously holding your forearm parallel to the ground and the divining rod (coat hanger ) also parallel to the ground. Turn on the sprinklers (yes, you're going to get wet ... ) and start walking around. Running water creates a magnetic flow that the divining rod will pick up, swinging into line with that flow. It will be obvious when it happens. You could practice by using a garden hose first if you want to get the feel for it.
Then there are companies that will come and find any buried utilities to make sure it's safe to use equipment to dig. Generally, this is a free service when used for finding utilities, however, for your purposes, there will likely be a charge IF they will even do such a thing. It is possible, however, that they would have a lead to a company that does.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!