Trouble with #6

I am at a loss. We utilize an electric fence on our home place to keep the livestock in. It will give you a pretty good jolt if you happen to touch it, believe me I know. Now here is the trouble, I have one cow who seems to be completely immune to the fence. There is one section where she simply walks through. That would not be be bad enough except now she thinks that she is now at the buffet table. She drifts from the round bales to the small square bales that I have in the hay shed. She must know who irritated I get for she has gotten to be sneaky about it. She waits until I am done with morning chores and then decides that dinner is served. The dogs do a great job of keeping her in, if they realize that she is out. She has gotten good enough that she is able to dupe them most of the time as well. I should not be surprised for she has been this way even when she was young. The first spring when she became old enough to realize that the grass is greener on the other side she was always out. Even when I turned the fence on and she zapped herself three times she still has not learned, or she has become immune to it. The snow on the ground acts as a great insulator and obviously she has learned this. Spring will be here soon and the snow will be gone and let's hope that keeps her in.