Turtle MIA?

I have a few turtles in the pond, most stay put but I have one bigger
one who refuses to stay in the pond! I have found him about a dozen
times buried in my flower beds. ANyway why does he continue to do this
i know they hibernate but I would think since its summer that it cant
be to cold! He eats and suns when I find him and put him back in the
pond, but he always ends up getting out and burying himself somewhere!
Right now I dont know where he went, he usually hides in the same two
spots but this time he changed it up to confuse me and I cant find him
anywhere. I dont want to fence in pond since I think that would be
unsightly, but wondering if there is any keeping a determined turtle to
stay put? Any ideas apprciated--and I you know where he might be hiding
please let me know--lol