Unlike the movie, Fielding didn't have surgery until years later. He went to the Cleveland Clinic right after Gonker passed away in 2003 and underwent surgery to remove most of his large intestine. This was roughly five years after Gonker was lost for two weeks in 1998. The movie condenses this and has him having surgery after he passes out in the driveway following his reunion with Gonker, a dramatic moment that didn't happen.
Gonker really did the donut trick. This impressive feat is in the Dog Gone book. Gonker loved donuts and would eat them by nudging the donut along the ground until he could get the tip of his nose inside of it. He would then throw the donut into the air and catch it in his mouth as it came back down.
One of the differences between the movie and the Dog Gone true story is that in the movie, the dog is a Yellow Lab, but in real life, the missing dog Gonker was a six-year-old Golden Retriever mix.
Goof: At 13'40" runtime, the name of the Virginian city of McLean, VA is misspelled as "McClean", possibly as a joke in connection to the good people working at the CIA, which is located nearby.