My father (who has Lewy Body Dementia) does not use too many power tools anymore (can't find them or figure out how to operate them) but can still use the lawn mower, which he enjoys.  He has a history of being a very physically active gardener and likes to climb on ladders, dig for hours in the sun, etc..  I guess we have handled this problem by closely observing and noticing when things change.  Sometimes I have to actually see how he does something to know whether it is safe for him. (I don't live with him).  For example I am suspecting he is currently losing his cooking skills, but am not there when he is cooking, so I need to spend some time there at the right time of day to observe what he is doing to determine if it is safe.  Can't get him to stop climbing on ladders completely, but did get him to agree to only do it when someone else is there to hold the ladder and to call 911 if needed!