Moose, the dog who plays Skip, is best known for playing Eddie on Frasier (1993). He died of natural causes in June 2006.
There are two separate scenes where it looks as though Skip is hit. One of the first is where Willy hits him with his hand, and another time by Junior Smalls, who lifts a shovel to hit the dog--a stuffed dog stands in for our canine star. Afterward, the real dog was put on his mark by the trainer, and the rest of the scene was filmed. After the shovel incident, we find Skip lying on the table at the vet's office. He has a cover over him and lies breathing heavily with his eyes closed as his trainer gives him verbal cues. When he awakens, he is told to open his eyes and lick Willy's face, and he happily obliges.
One of Willie's friends in the movie is named Spit McGee. This was also the name of one of Willie's cats as an adult, and his life is featured in the book "My Cat Spit McGee"
Director Jay Russell wanted a smooth-haired fox terrier to play Skip, the same breed as the original Skip, but he couldn't find trained ones. Early in pre-production, he used a dog with no acting experience for a shoot of second unit-type footage and quickly found difficulty in doing even basic things, like keeping the dog in the frame. He concluded they needed dogs trained in acting, so similar-looking Jack Russell terriers were used (at 07:00 in the director's commentary).