I worked for a company out of Columbus Ohio that did this. They were using a quick couple that would open itself. It was a known problem from the manufacturer, supposedly the coupler manufacturer came out with a fix and they still had the problem occur. The end result was two guys being killed in the trench in two separate incidents. The last one being the most disturbing as the guy survived for over two weeks after, but died from an infection.

Company solution was two fold. 1 Remove all couplers with known defect, and instead of selling them, they were cut up for scrap. 2 Add lifting hook to all new couplers. This provides safety system attachment point. All buckets had a D ring welded to them, that has a chain or cable that is connected to a lifting ring. The ring is attached to the lifting hook of the coupler. The company patented this system, but shares it to anyone, included manufacturers and competitors for free. The system is also installed on all front end loaders with quick couplers.