My neighbors say that an outdoor cat will keep snakes away from your house. The cat doesn't kill them, at least not the large one, but the cat does annoy them until they leave. I have an indoor cat, and can attest to them being annoying.
Back to roundup: Our governments, local, county and state, use roundup to poison the edges of uncurbed streets, fence rows and around the bases of signs. One would think the State of Texas has to comply with some strenuous regulations before spraying at random from a specialized 1,000 gallon truck.
I don't know enough about life science to make an educated statement about the harmful effects of roundup, but I do know there is a lot of it being used in my tiny, little agricultural surrounding.