Shortly after finding the fourth dog's body, the men caught a fleeting glimpse of one of the wolves.
"I looked up and saw a wolf pop out of the brush, about 40 yards away from us," Derrick said. "McGuire yelled at it, and it was gone in a blink."
Derrick estimated the wolf's size at 120 to 150 pounds. "It was bigger than the biggest German shepherd you'll ever see," he said.
The wolves - Derrick and Harrison believe there were four to seven of them - killed eight beagles and injured another in what Derrick calls "the blink of an eye."
"In 15 to 30 minutes, there was nothing left," he added.
None of the men were aware that wolves might pose a threat.
"We knew there were coyotes in the area, but I hadn't heard anything about wolves," Harrison said. "I'd been going up there for 16 years, and the worst thing that had ever happened was the time a couple of our dogs got messed up by a porcupine."
After the attack, the men started asking around about Upper Peninsula wolves. What they found left them determined never to return to the area.
"Michigan's wolf management plan calls for a population of about 200 to 300," Derrick said. "The population right now is estimated at 670 or so."
Pressure from animal-rights groups has hindered Michigan wildlife officials' efforts to reduce the population through hunting. A hunt will be held this fall, but will be halted after 43 wolves are killed.
"I don't think any of us are going back," Derrick said. "There's too much risk to the dogs. If there's a chance for something like that to happen again, we probably should just stay away."