I got a new vet after the messup with my beloved Collies. The old one insisted on yearly boosters, had to put my large male to sleep 5 years ago after he got real ill. He also had hip dysp. Then a year later had to put my other male down - two tumors one on his prostate, other on the bladder, 2 years later my Lady was put down.
The new vet is on the 3 year boosters, this next time is the last with the boosters - except Rabies. My Shelties are just over 5 years old now.