Something else you could try is a side-slip ( I think that's what it's called). On final, give rudder in one direction and aileron and elevator to keep it straight. So you give right rudder and enough left aileron. This will increase the drag and should slow the plane down. I've done this before to lose altitude. If your trying to slow the plane down so it will be easier for you father in-law to land, this wouldn't be the best thing to do. In any case, good luck!