train the ducks to chase after the enemies. Lol

Build an exact replica of that area right next to the original. They’ll be confused, are they visiting the real ducks or a simulacrum of the ducks?

“There is at least one more bear trap on my grounds than you can spot.”

depending on where you’re from you can hang up a sign saying “trespassing Children will be converted to Islam”

I would have to go with landmines. If that isn’t enough of a deterrent, and claymores or even some bouncing betties.

Give the ducks a nice shower/sprinkler set up that’s both timer and manually controlled.

You’re looking at this wrong way.
Buy a gumball machine. Put on fence. Fill machine with enough feed for the day. Charge other people to feed your ducks

Trespassers will be trebucheted.

"Entry Fee (min one):

• Carrot
• Apple
• …"

That way you get duck (or human) food for free.

Obvious answer is to give the kids ducklings for every visit. Pressuring kids parents to stop their kids coming over without permission. Unless they want to own duck pets.

Get you some geese

Pro tip - feed them a handful of dandelion leaves twice a day, they’ll be your best friends

Build a moat. It would certainly keep me out.

Put up a sign that says “WARNING: rabid ducks, enter property at own risk”