Why do you need to halau them? They not permanently there

If they litter then can tegur them and tell them the upper hand that you own the land and already nice enough to let them fish and you just want the place clean.

They just wanna do a harmless hobby

I suggest to take this opportunity into a business

Open a fishing supplies shop at their usual spot.

Or sewa some chairs for them.

Opportunity cost:
which investment or expenditure will yield the most benefit to me.

Spending to fence up my house
Or convert my house to capitalise on their presence and needs they have.

If fencing up is beneficial at a cost I’m willing to pay for. Sure go ahead.

Back to the case, it is a pond where there is source of food. Mother Nature provided the pond with fishes and the owner is not making use of it at all.