When Shadow falls into a pit and injures his leg, the dog never actually fell into the pit. When he stepped on the boards, they broke, but there was a platform immediately below. Then a fake dog was dropped into the pit and these scenes were edited together. Shadow tries to get out but the pit is large and deep and muddy and he keeps slipping back into the pit because he cannot get a good grip. To accomplish this scene, a special pit was dug which was about three to four feet deep. For the sliding back and forth, one trainer was at the top of the pit calling the dog. Another trainer was at the bottom telling the dog to stay. When he did, he would naturally start sliding downward. The dog could actually walk out on his own at any time and did so several times during the filming. When Shadow does appear at the end of the film to be reunited with Peter, Shadow runs with a limp. This was accomplished by putting part of a round wooden bead between the dog's toes. The bead did not hurt him in any way, but gave him a peculiar sensation, causing him to walk with a limp.
This was one of Don Ameche's final movies before his death the year of the film's release. He voiced Shadow.
Chance running full throttle into a sapling and then continuing to run (specifically the part where Chance implies that Sassy is fat when rushing off for breakfast) was done completely by accident by the dog actor. They thought it was somewhat hilarious, so they kept it in. Similarly, Michael J. Fox and Sally Field adlibbed the lines right after Chance ran into the tree. Similarly, Chance stumbling when running through a field was given a humorous line. "Whoa! Gopher hole!"
Chance loves to tease the aloof Sassy by chasing and teasing her. The chase scenes were done in cuts. The cat was merely running to a buzzer while the dog came in response to verbal cues and was not actually chasing the cat.
When Chance jumps out of the car, he bangs the youngest child's head on the door hard enough to make the camera pan off him pretty fast.