Mines work. That is why they are used.

That said, I would support research into developing mines with some type of "expiration" mechanism, that would render at least the firing mechanism inert after a set period of time. The ideal would be to have the chemicals of the explosive charge itself eventually decay into harmless compounds. I am not a chemist, and don't know if this would be feasible. Some exterior sign that the mine has "rotted" would be very useful, like a color change or something.

Worst inconvenience to the military would seem to be having to remine an area after a few months to a year or so, and of course, the mines would be more expensive and hard to make.

I'd like to think at least the U.S. is already looking at this.