Most IED's are triggered remotely, and mobile (cell/sat) phones are a favorite ignition tool. IED's can be hidden out of reach of flails. Mines have a vast array of ignition mechanisms, not just pressure-sensitive methods. There are magnetic mines, time-delay mines, mines that need circuits to be connected by the likes of sappers searching bayonets.
There's one highly satisfactory way to eliminate IED's - and that's to promptly and regularly eliminate from this world, those who plan, design, build and detonate them.
Then there are the "entrapment" mines or IED's. The nasty buggers set off one charge to create some damage - and as soon as more people arrive to help, they set off other hidden charges. There are often mines hidden under mines, set to trap those who defuse the top mine, and as soon as the top mine is lifted, the bottom mine, or IED, is activated. There is no end to the methods of evil. I can regale you for an hour on the inventiveness of the SE Asians when it comes to IED's - the perfectors of IED's. The current crop of terrorists have only learnt from the NVA and VC - but they have more technological tools at their disposal.
Highly sensitive explosive sniffers will likely be the tool of the future.
Super-sensitive explosive detector developed - tech - 13 April 2005 - New Scientist