Kong makes a lot of interactive toys. I use the regular classic Kong and put some kibble in it and 'seal' it with his wet food then freeze it. It keeps him entertained for a bit. Frozen yogurt is also okay, just make sure it's plain and non fat, many use Greek yogurt. Kong has other things as well.
Nina Ottosman has a lot of different dog puzzles to keep them entertained too.
Or you could make something like this LOL!!!