Habitat - Outdoor :: Transferring my turtles to an outdoor habitat

[Sara'sTurtles]

I have had three RES for 10 years. They are currently living in a 75 gallon tank, fully equipped. I'd like to move them to an outdoor pond. I am in Maryland, and the summers get hot here. The winters get cold. In the spring, I am going to begin construction of the pond, and won't move them until Memorial Day weekend, when I know the weather will be warm enough for them. I plan on putting basking rocks in the center, so they cannot escape. They are good about submerging when I approach the tank, so I don't think they will be prone to predation.
I want to know what I need to ensure that they hibernate properly when the time comes.

[Linus]

Hibernation is always risky. I live in Southern California and let my RES hibernate. But it doesn't get that cold here.

I recommend having some predator protection. I've lost two turtles to raccoons. So we now have a gate over the pond. Raccoons will go swimming if they need to.

[Sara'sTurtles]

Ahh, I see. Thank you!
I have a friend who has a beautiful turtle living in an outdoor pond and she winters every year from late October to early may, and she's right here in Maryland. I'd love to pull it off.
Do you think turtles have an instinctive drive to winter once it gets cold? I'd keep an air pump running so the water won't freeze over, and I'd put some mucky substrate in the bottom so they could make a den for themselves. There are tons of turtles in the wild here, and they all must go somewhere for the colder months.
As far as predators of, I can make a netted tent over the pond so they still get sunlight, but can get nabbed by any hunters.

[steve]

How big will the pond be?