Hell you still find explosives from WW2 all over. It really is difficult.

WW2? We're still finding explosives from WW1 in Belgium

True that. I used to work in the Netherlands, and sometimes it seemed like every other week the rail network was disrupted by a newly-discovered unexploded bomb, left over from the plastering the Allied air forces gave the Dutch railways.

Indeed. With landmines from 90's at least general areas are known, there's signage and if you're not being stupid by venturing way past signage it's all really safe to be around.