I use a butter knife to stuff the kong with pb or cheese whiz or whatever. Plug the small hole with pb form the outside, then add treats in the other end, stuff with more pb(or whatever you use), add more treats etc and finish off with pb. I stick a biscuit in at the end so it sicks out a little.
I also use carrots and apples along with kibble and dog treats.
Never mind the dogs, beware of the owner!!!