The best way to encourage a hen to go broody I've found is to let her accumulate a pile of eggs; eight seems to be the bare minimum here. Once she has say ten eggs, take a couple away. Believe it or not a hen knows exactly how many eggs she has. When you take a couple of eggs away it seems the hen realizes that her eggs are no longer undiscovered and safe. Ime this encourages them to sit on what they have left.
The method is far from foolproof but I've had it work enough time now to believe there is some merit in the logic and method.
PS, I don't believe golf balls will do the trick. The chickens here at least are not that stupid.