If you don't have a proper fence, people just assume it's public property that they're entitled to use (because if it was out of bounds, it would be fenced, right?)
This is why, the world over, all land gets enclosed and fenced eventually. If you are in Britain, a tall hedge gets planted for good measure too.
Our area, although not fenced in, is clearly occupied and private land. Even where the campers put their tents, there is a hut, and my wife and I have grown several plants and landscaped the area. Land disputes and land thievery are far too common in Cambodia, so the rich often feel it's not illegal to tread upon poor people's land, but if I waltzed into their luxury villa in the capital, the police would be called immediately. Even our nextdoor neighbor stole some land from her neighbor on the other side, building her bathroom and beer sign on his side of the property while he was out of town.
It's horrible when neighbours are like that.
If I were you, I'd put a fence up as soon as you can manage it, and plant a prickly hedge on your side of the fence.
Does Cambodia have the equivalent of holly? Or could you plant holly in Cambodia? It's a proper deterrant to intruders, but looks good.
I agree, our prickly hedge will be a row of tightly spaced cassava followed by bamboo. There is a thorny plant here called "touch me not," and it is covered in little thorns, and we already fight it every day, but it does have beautiful flowers.