Keeping your fescue at recommended height (4") and fertilizing in the fall and spring will shade out bermuda and slow down its expansion to something manageable. You really see bermuda take over when your cultural practices encourage it- mowing too low, adding too little water, or fertilizing out of turn or at an inappropriate rate

if you use herbicide you need to just commit to it. Most effective thing I have ever done is kill it (6% glyphosate) just before peak growing season, let the roots come back toward the end of the season, then kill it again. If your timing is right and you have a little luck you can get a cover turf growing for the next season and be done with it in one year. Bermuda roots can be extremely deep so it's able to hunker down in adverse conditions especially if you are lackadaisical about herbicide.
[Post edited by typed by ben at 04/12/2020 07:43AM]