In an area where £10 might be enough money to pay for a doctor's visit for a deathly ill child, or feed a family for a month, you'd probably get a lot of people risking their life and getting killed to get their hands on just one landmine, which strikes me as a singularly inefficient and cruel way to try and clear those fields.

iirc, The British did this in India but with snakes.

It wasn't long until the locals just farmed snakes to sell to the British.

Plus, retrieving landmines would be a pointlessly dangerous task, when all you really need to do is blow them up when nobody is around.

This creates an incentive to clear only first few mines, because they will become progressively harder to find and an hourly reward rate would quickly fall to near zero.