Please consider allowing healthy, active dogs 12 years of age and over to continue to compete in UKC's Weight Pull program.  Possible accommodations to provide a safe environment for these seniors is perhaps Veteran classes (much like Agility), capping the max % they can pull to a lower %, and requiring a health clearance from a veterinarian for every year the dog continues to compete.  Weight pull is the only sport in UKC that has an age cap, even though it is considered by many professionals to be one of the SAFEST dog sports.  There are many senior dogs who enjoy competing well into their teens and are physically able to do so without issue.  There are other organizations that allow seniors to successfully compete with vet clearance, without any harm coming to the dog.