In senior dogs, sudden humping can be linked to urinary tract infections (UTIs), skin allergies, or even discomfort from arthritis.
If the behavior wasn’t corrected in their younger years, it may simply be an ingrained habit they revert to when bored. How to Manage the Behavior
Always consult a vet first. If the humping is accompanied by licking or frequent urination, an underlying medical issue is likely the cause.
Mature dogs still need to work their brains. Interactive puzzle toys or short training sessions can reduce the boredom-induced humping.