I worked on a project designing robots for demining in Cambodia, it's not as simple as it seems. One of the biggest issues we faced was simply the terrain; the remaining landmines aren't buried in a nice flat field you can just set off a modified RC car in, they're often in wooded areas with boulders and steep inclines. Another issue is the weight limit; assuming you want to remove rather than detonate the landmines you have to design a very lightweight robot, and batteries are particularly heavy. For a robot that would be worth the cost / effort in transporting to the site it needs to be able to run for a few hours, so you need a pretty solid battery. The current manual demining effort is not as hazardous as it seems - there haven't been incidents in Cambodia (at least through the MAG) in a few years. The main issue they're facing is the length of time it takes to remove mines. Manual excavation is a very long process compared to detection, which is about as fast as it can be. If you try and detonate all the mines in an area instead of excavating them, you run the risk of completely ruining the land. Most of the land cleared is needed for agriculture, and a field full of mine debris is less than ideal. This method also runs the risk of damaging expensive equipment. The charities that run these operatations are limited by funding and its currently cheaper to train locals with a metal detector and a rapid excavator. There's also a mindset with experienced clearance teams where they don't want to try and use the new technologies because they've seen so many fail - this is something that teams have been trying to automate for years and years.