[grandmatoall]

Are you taking him for a walk? They need that exercise to keep their brains motivated and their weight down. Like us.. they get bored when their environment never changes.
Have you considered play dates with another dog? Is there a doggie park around where you live?
Others may also have some great ideas.. the best of luck to you.

You might also try treat balls.. where they have to work at getting the treat out.