How can I help my 25 year old from talking so much on the job?

We have a Landscaping Business for about 10 years now. He has been fired before. He is a hard worker though. We just don’t know how to get him to listen and talk less. My husband tells him over and over again, but he still doesn’t fill things out right. I am always blaming it on his childhood. He had to live with his dad and I divorcing with two other siblings. He doesn’t get it though and it seems like he doesn’t realize things when he does it. I need help so he doesn’t get himself fired because I just don’t know where else he will work.