Rat terriers from hunting stock usually make fine squirrel dogs. I am going to try to post a photo later of one that I hunted along side for over 12 years. This dog, "Bullet", is now 17. He belongs to a great friend of mine, Huie. Just this week Huie and I and our wives sat down at dinner and the conversation came around to a wonderful trip to hunt squirrels where Bullet and my Dachshund Tex spent most of the day working hardwoods for squirrels. That was 14 years ago. His son was a kid then. We had 5 hunters and took the limit .... 60. Tex is gone long now. Bullet is now very hard of hearing and his eyesight is no longer sharp enough to spot squirrels moving through the trees. Huie has retired Bullet.
Since Tex, none of my Dachshunds since have shown any interest in tracking or treeing squirrels .... but Mojo's son and grand nephew of Tex that I gave to my brother in law as a pup is an ace squirrel hunter. "Grizzly" will track and tree til he drops from exhaustion. And like Bullet and Tex, if Grizzly is looking up and barking, there is a squirrel in that tree somewhere !