get ahold of "JAKEN" who is a forum member. he makes and ships very fine custom made probes. the ones you get at hardware stores and electric supply houses are not well suited for probing privys. measure from your solar plexas to the ground, this is the best length for a probe.
If you're looking to make one, skip the chain stores, they don't have the right stuff. Go to a junkyard or a metal supply shop, only use spring steel to avoid bending. The hood or trunk spring/supports works well, older cars=longer steel most of the time.