In answer to the fencing questions--I've had turtle ponds for about 7 years now and my fencing has always been 1/2 inch mesh by 2 feet wide galvanized screen cloth.
My ponds have always had a walk-around area of at least 2 feet all around the pond except where it met the water course that I also included in building the pond. I excavated a ditch 3 inches deep and 4 inches wide and bent the mesh 4 inches to fit in the ditch turned in facing the pond. That way, when and if the turtles tried to dig at the fence they could only dig down 3 inches and they would hit the buried mesh. That, to me, is a much easier way to go than digging down 3 feet. For my Box Turtle enclosure, I made the trench 5 inches deep and 5 inches wide and bent the mesh to fit, as Boxies are known diggers. I bent the top of the mesh over facing the pond and with a tin snips, cut the 3 inch bent over part at various places to allow for the curve around the pond and forgot to say I cut the bottom bend also(much easier to make a circle that way). Now keep in mind that I also use either 5 inch or 6 inch Black plastic lawn edging all around the outside of the fence. This is to deter the turts from seeing distant vistas and from trying to go through the fence. If they can't see beyond the edging they won't go there. All that has worked fine except for my young turts that climbed the mesh but they were brought up short when they hit the bent over part of the fence. When they fell off the fence, they only had a few inches to fall and the fall was cushioned by the grass. My ponds are preformed, in a hour-glass shape-the length is 8 feet, the 2 wide parts are 4 feet and the waist section is a bit over 3 feet. The water depth is 18 inches which is deep enough to accomodate planters with lillys and on the underwater shelves there are planters with reeds. I float Water Hyacinth and Water Lettuce all season long to help control the algae and for food for the turts. I also keep 30 or so Black Trapdoor Snails in the pond because they eat all the turtle waste and decaying plant matter. Also have a 7 inch Comet Goldfish and a 5 inch(for now) Koi and they vie with the turts to be first fed.
Holy smokes! I do ramble, don't I? George