If he is competent you cannot get control. If he is competent and he is refusing care, that is his right.
Often in this situation you would need to wait for a major event to happen, something catastrophic like a fall, or a delusional breakdown, to call an ambulance and have him taken to the hospital.
Christi903, one thing to try is to tell Dad that if he doesn't have an annual checkup with a doctor that he will lose all future medical care..... I know it is a fib, but sometimes we need to do what is called "therapeutic fibs" to get our elders to do what is in their best interest.
Often in this situation you would need to wait for a major event to happen, something catastrophic like a fall, or a delusional breakdown, to call an ambulance and have him taken to the hospital.
Angel