My husband and I are in the green industry (that's green as in landscape, rather than green as in taking care of mother earth). Hubby has a running gag, whenever someone has a problem in the yard, he'll say, "I have a chemical for that!" It's a joke, because we try to keep the chemical use to a minimum. We will explore all possible options before reaching for the sprayer, because we have a great deal of respect for what these chemicals can do. Just because you don't need a license to purchase or apply it, doesn't mean it's completely harmless.
I'm sorry, but the OP's husband sounds like my FIL. He knew what was best, never mind the label. (FIL put himself in the hospital once, self-medicating with aspirin to prevent a heart attack). Roundup does not belong in a garden. It can move through the soil, destroying the roots of the non-target plants you were trying to grow. During hot weather, it can vaporise, and damage the foliage of nearby plants that it wasn't sprayed on. If sprayed on plants that are drought stressed, it will be poorly absorbed, most likely damaging but not killing.