There are literally dozens of ways to set off IEDs. They can be remote detonated, command detonated, set off by weight, set off by tripwires, or by timers of some type although from what I understand those aren't being used much over there now.
The most sophisticated and lethal variants are being smuggled in from Iran.
L
My solution? Do what the Israeli's used to do..blow up houses. When an IED goes off, after the clean up, blow up the nearest house after it gets evacuated. That'll put new meaning into the words "neighborhood watch"!