Can I physically force my father to bathe with the assistance of an attendent?

My father, 88, has been diagnosed with dementia and has recenty fallen, broken his hip but has surprisingly been able to walk quite well with the assitance of a walker. Before his fall, we were having serious issues with his personal hygiene (i.e., he would go a couple of MONTHS without bathing fully). When he was in the rehab facility, he was bathed regularly by an aid. Now that he has returned home, the old habits have returned and he becomes physically and verbally aggressive if you try to force the issue, with all the kindness and calmness available. It is always, "I'm going to do it later". I have tried changing the times to see what best suits him, change the towels, the lighting, he has a transfer bench he can use so he will not fall, a hand held shower, a space heater so he doesn't feel cold....every kind gesture, security measure or coaxing you can imagine has been done and he simply refuses. My concern is the surgical wound from the hip surgery and the risk of a bacterial infection. I do have legal and health POA over him. When does it become mandatory that he HAS to bathe to maintain his own health? If he does not bathe and suffers physical consequences because of this, can I be held responsible? Can he be made to take a shower against his will to safeguard his health and safety?