Danene Brown and Darryl Powell thought adding a third dog to their home in Richmond, Va., would be easy; the first two were a cinch to train. But when the couple picked up Hopper, a French bulldog puppy, last February, that assumption was almost immediately challenged.

“The pandemic made it nearly impossible to socialize him,” said Ms. Brown, a physical therapist, and Hopper developed a “Napoleon complex.” “Any time that we would try to introduce him to another dog on a walk, he was aggressive and protective of us and didn’t know how to play well with others,” she said.

Ms. Brown and Mr. Powell met with Melanie Benware, a local trainer and the president of the International Association of Canine Professionals. “People are going out less,” Ms. Benware said, “therefore their dogs are not being exposed to as many people, dogs, sights and sounds.” She taught the couple how to train Hopper to respond calmly to other dogs. “He’s gotten better, but he’s still a work in progress,” Ms. Brown said.