lol, I can't believe they've never had a Kong!?? Tillie gets one when I leave for work every day. I don't "fill" it with pb. I actually put 1/2 of her breakfast in it (feed her the other 1/2 first thing in the morning) and then top it with pb. it's probably less than a 1/4 tsp of it.
I have never worried about giving it to her. except it gets stuck in her beard sometimes.
I often times vary what I put in the Kong, but it is always something healthy. either her regular food, or some banana chunks (topped with pb), some frozen peach puree (topped with cream cheese or yogurt), dried salmon, some sweet potato puree, red bell peppers and mozzerella cheese (her FAVORITE). I don't 'stuff' it full by any means and if I have time, I prefer to freeze it so it gives her a little extra time working on getting the stuff out!
She isn't a huge chewer, so this is actually only the 2nd Kong she's had. The first one was the little puppy one! Although she is totally due for a new one as the rubber is starting to get a little frayed...