This can be a tricky situation for many. Your father most likely views yard work as a way to maintain his independence. Although it’s detrimental to his health, he sees this as a way to lead a normal life. The truth is, he just isn’t as young as he used to be, so be sure to stress the importance of making sure he rests every once in awhile, and if you need to, hire a landscaping service or neighbor to take care of the yard work.