I am going to build an enclosure for my Russians in my existing garden. Mostly I grow weeds for the last few years anyway. It is a large garden 20' X 30', 3 foot picket fence. It is in my fenced backyard. I was planning to line the inside of the fence with railroad ties. Two high and cap the corners. Will I need to bury something to prevent escape or line the ground with rocks? I know they dig and bury themselves, but do they tunnel out? I have heard so many escape stories, I am completely paranoid about putting them outside.