How can you keep unwanted bushes, etc from growing back?

Here is an article that might help you - https://www.texastreetrimmers.com/how-to-prevent-shrubs-from-growing-back/

Pull them out may need small bob-cat depending on size or cut back then Use Round-Up on remainder. You do need to leave some greenery on plants because round-up get absorbed thru leaves into trunk into root system & doesn't work as well if plant is dormant. I'd get concentrate & mix stronger than directions 1/2&1/2 .Round-up is no different than other pesticides(flea,mosquito,tick control even ones we put on our pets)herbicides even fertilizers we use everywhere. Just follow safety instructions Spray with nozzle down on plant you're trying to kill,don't use in wind/breeze,don't get in wet spray,use gloves.Put some food coloring in sprayer so you can see where you are spraying or spilling. May need to repeat the spraying until no new growth,depending on how big trunk root system is,and as I said if plant is dormant it needs to be growing for it to work correctly.

Sue, I’m afraid you will need to dig them out of the ground. If this is hard for you, dig a little at a time, near to the bushes and out a foot from each one. You may need to tie a rope around the bus or the roots, then pull the bush out of the ground. Some people use a car, truck, or tractor (or bush hog) to help pull the bushes out by the roots. But another way is to cut the largest roots with an ax or saw so you can pull them out easier. Best wishes on this one! ☺️

Sue: I have used salt with quite a bit of success. (Use a lot... epson salts are cheap.)

no weed killer its not needed just dig them up roots and all