The back forty sure looks nice. Have you ever thought about spraying around under the fenceline with Roundup? It'd sure cut down on all that weedwhacking.
I've thought about poisons for various things, even bought them, but I've always been leery of using them in any kind of widespread way. I'd have to poison about a six-foot wide strip, because that canary grass is so tall, if I don't cut it wide enough it just falls in toward the cut and gets in the fence anyway.