I’ve had success with the Kong Extreme, as well as the Zogoflex Huck. Fill a Kong with peanut butter and then freeze it. It’s a great thing to keep them busy while they’re alone for a couple hours.
The other thing I do from time to time is pick up old soccer balls. The local lake is littered with them, unfortunately. I try to ‘recycle’ one every time I paddle on the lake. My dog shreds them pretty quick, but they’re free and easy to come by. He loves them.