My driveway lights have been working well for a year and a half. About two weeks ago, the circuit breaker started tripping after about 10 seconds when I turn them on. I have checked to make sure the wires are not wet wherever there are connections and have replaced the switch. Any suggestions?

What kind of lights? Incandescent? What size lamps? What size breaker?
is there anything else on that circuit?

Assuming that nothing has changed with the circuit load, is there any chance that there has been any digging or work that might have damaged the underground wiring?

It would also be useful to know how much current cicuit is drawing, but this should only be attempted if you are comfortable around power and meters--as this can be a dangerous task.