As a follow up question, how are the farmers/owners of that land compensated today? Battlefields of WW1 are still claiming victims and damaging property with exploding ordinances.

Wouldn't this not be covered under insurance as acts of war are pretty much never covered? Or is there a special fund or type of insurance these landowners can purchase/use?

Since there are still unexploded ordinances across many of these former battlefields, how big of an issue or concern is it for the general public in these locations?

I'll talk about Belgium as that is the area I know best. First of all, It wasn't just farmland, cities were destroyed as well. Have a look at Ypres. It's safe to say that there are pretty much no buildings left in the frontline area that date to before 1914. The "medieval" buildings you see now in Ypres have been painstakingly reconstructed.

The rehabilitation of farmland was a long drawn-out process that took many years and a lot of manpower, as you can imagine. The fields were riddled with shrapnel and other debris to the tune of several thousand kilos per acre. And then there was the unexploded ordinance, for which the army established the Ordinance Disposal Unit. They are still at it 100 years later. About 10 tons of unexploded ordnance is cleared each year in the "Westhoek" alone (the tiny Western part of Belgium unoccupied by the Germans in WWI, where all the trenches were, now mainly farmland). At Poelkapelle, also in the "Westhoek", there is a special facility for dealing with chemical and poisonous munitions, established in 2000, since when they have gathered around 40,000 pieces, of which they have so far disabled or destroyed 11,000.

Nevertheless, many farmers started returning to their land in the immediate post-war period. The Farmers Association (the Boerenbond, a private Catholic entity representing Flemish farmers' interests that was founded in 1890) offered basically free loans in anticipation of the German reparation money. For several years work crews numbering tens of thousands were sent from all over the country to help with land clearance. The Ministry of Agriculture provided cheap seeds, fertiliser, and livestock obtained from abroad, sometimes through donations. A lot of farm equipment was requisitioned from Germany, partly because the Germans had taken Belgian farm equipment out of the country and partly as war reparations.

So to sum up: the farms were reestablished through the efforts of the Belgian population as well as donations from abroad and reparation payments from Germany.