Okay, I just read your post on the Gen forum.
I spend a lot of time browsing livestock forums, and wormers are of great interest to me.
That said, Panacur is very safe. Yes, the Heartguard will protect against reinfectation, but you also might want to clean up your yard area, especially if you have stray or visiting dogs coming through.
One thing I've done in the past is pour small amounts of bleach on poop areas :roll: . General yard hygeine will really help.
I don't think you need to call the vet. Panacur really is considered very safe, and it's likely the loose stools are from something else. if it continues, though, give the vet a call!