I live in the southwestern part of Texas where we have some major issues with exotic grasses including Bermuda, KR Bluestem and much more.
We are in the 25+ inch rainfall zone. In the past 5 years of extensive drought we have received no more than 18.7 inches in one year. In fact in 2011 we received 4.9 inches on our ranch. My point is Bermuda grass can and will survive anything. We use a very similar method of
gardening: we built 4 ft wide raised beds by hand (40+ ft long) with about a 3 ft walking path. Like I said all dug by hand and during that process we literally sifted through every pile of dirt and removed Bermuda grass roots. 2 rows of drip pipe top each row with anywhere from 4 to 8 inches of wheat straw mulch. GUESS WHAT? Regardless of our extensive efforts the Bermuda grass was back strong withing one year. We fought it as it came up in various places, but it won the battle.
Other methods we have found useful: during the Fall months we cover crop heavily infested areas with a mix of wheat, oats, clover, turnips, and winter peas. This seems to choke it out during the spring when the Bermuda grass comes out of dormancy. Doesn't fully solve the issue, but alleviates the problem.
My best advice is to keep your garden covered in something. Whether it is plants or mulch. The best way to fight Bermuda is to out compete it on the phototrophic level.
Plowing won't resolve the issue, and neither will mulching heavily with cardboard and straw (we tried sheet mulching too). It will just take a little longer to come back. Once you have it there is simply no getting rid of it. Do your best to protect your garden borders. Perhaps a
chicken run around the entire border to keep it beat down. Or shade it out along the borders with dense
trees and bushes. Bermuda doesn't like to be shaded! In fact you will not find it growing in heavily shaded areas.
Just some ideas. I hope they help. Don't resort to chemicals because they don't solve the long term issue either (also learned from
experience long ago).