The defensive pair have inked two-year contract extensions to keep them at the Perth outfit.
Saints boss Derek McInnes was delighted to secure the futures of the pair on long-term deals.
"We are pleased to get Garts and Ando signed up," McInnes told the club's official website. "We are looking to get one or two things sorted out over the next few weeks.
"I'd like to add a few more to the squad over the summer. The players have done very well this year but like every manager I want to improve every season."