I swear by Busy Buddy Twist & Treats. Here is the URL - you need to scroll down about halfway to get to the Twist & Treats.
https://www.premier.com/store/Produc...x?cid=3&pid=34
I stuff them with canned dog food, tuna, salmon, etc. put them in baggies (to control the leakage) and FREEZE THEM. It takes awhile for Zack to work his way through them but somehow he manages to lick them clean. You can control the amount of space available for tongues by twisting it down part way or most of the way down.
Also works great for teething puppies. The frozen toy really makes them feel better.