Unfortunately after your turtle has escaped there is little chance he/she will come back. hopefully your pond is the only source of water around because that could lure your turtle back. but just because your yard is fenced in doesnt mean anything. turtles CAN dig holes! the only way to ENSURE your turtles will stay in the pond is to put a fence around the pond and make sure there is NO possible way the turtle can escape. i wish you good luck in finding or luring your turtle back, but i dont know of a way to lure a turtle back. i would say your best bet is to make sure there is always water and ample food in the pond if the turtle should decide to return. good luck and best wishes 
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~ Evie 
Pets:
0.1.0 German Shepherd {Dusty}
0.1.0 German Shepherd/Collie mix {Shadoe}
0.0.2 RES turtles {Booger and Snot}
1.0.0 African Clawed Frog {Bingo}
0.0.1 Snail {Gary}