What's been one of the most effective ways to figure out where Taliban forces and other bad guys hide their improvised explosive devices in Afghanistan and Iraq?

It's not a dog or a ground-based technology.

It's a classified program, called Red Dot.

According to what's been said publicly, Red Dot involves the tactical use of signals intelligence (SIGINT) and measurement and signature intelligence (MASINT) satellites operated by the National Reconnaissance Office. As Matthew Aid points out, the amount of power that any IED could possibly emit is infinitesimally small, probably on the order of a large cell phone battery. That means that the U.S. can detect (probably) the unique RF frequencies associated with IEDs passively. I assume that our satellites have some sort of interrogation capability, one that allows it to "ping" the ground for objects that respond to specific frequencies known to be used by the Taliban. The energy associated with the frequency is orders of magnitude stronger than the power source itself. I assume that these satellites orbit as often possible, and relay information to the Coalition Intelligence and Operations Center, which analyzes them and dispatches specially trained counter-IED teams from the Defense Threat Reduction Agency and the Special Operations Command to neutralize them.