Once you have detected a pinhole leak in your copper pipe, and it is above the slab thus it is not that difficult to repair.

Isolate the leak, and turn off the water supply to the house, the supply can be either at the valve where it comes in or at the water meter located at the street. If you turn it off at the house then open the hose bib that is usually located just above the water shut off. This will relieve any pressure from the internal pipes, and the leak should stop dripping now.

Subsequently, you need to get some parts to stop the leak. You would need small piece of soft rubber and a pipe clamp, if it is a pinhole leak. Try to find a clamp that is close to the size of the pipe. You can usually locate this type of clamp in a hardware shop or auto parts store. Make sure the rubber is soft so it will close the leak when you tighten the clamp.

Do not over tighten the clamp or you may crush the pipe and result in a bigger leak. Place the rubber over the hole and lock the clamp. After it is tighten, turn on the water and check the leak. If it has stopped dripping then you are done. Otherwise, you have to tighten the clamp slowly until the leak stops. Again, do not over tighten the clamp. Hopefully this will be the last leak you will have, but chances are it will not be.