Although there are some vocabulary differences between what residents of different regions call a turtle, a tortoise, and a terrapin, one thing is for sure, when one of these is nibbling on your tomatoes you want them gone. While it isn't a good idea to just move the terrapins to somewhere else, you can construct a simple fence to keep terrapins from eating tomato plants and those red tomatoes that attract them. With the fence and some tomato cages or stakes, you should find your fight to harvest whole ripe tomatoes a lot easier.
Dig 1-foot-deep holes around the perimeter of your garden every 4 to 5 feet. This can be around the whole garden, or just the concentrated portion where your tomato plants are if you don't have one long row of tomatoes.
Place a post into each hole and firm up the soil around it so a foot of post is buried and 2 feet are sticking up from the ground.
Run the wire mesh from post to post around the garden, hammering in U-shaped pins or staples with the rubber mallet at the top, bottom and middle where the mesh aligns with the posts. The bottom edge of the mesh should be snug against the ground.
Place tomato cages or stakes at each tomato and train them to climb the cage. Use plant ties to help keep the main stem of the tomatoes growing up the cage or stake as needed.
Raise any lower branches along the bottom 2 feet of the tomato plants, and use plant ties to secure them to keep them lifted up off the ground. Use extra stakes if needed to secure the lower branches without breaking them off.