Can red eared slider turtles live in a pond?

Yes - provided they will encounter the same temperature range as if they were in their native country. Additionally the enclosure should be animal-proofed against possible predators (local cats, dogs etc) I recently had to treat a neighbours injured slider that she kept in an outside pond. She wrongly assumed it would be safe to leave it unattended in her pond. It ended up being attacked by a cat, and now has one foot missing and a cracked shell !