Some cats do not accept the presence of another cat in the household well. This leads to urine marking behavior and to aggressive acts directed towards the other cat. It is difficult to handle this situation as you have discovered. It is also difficult to change the situation. Keeping the cats entirely separate has worked for several of my clients but it does not sound like Doug is amenable to this situation, either.
Medications help in a limited number of cases.
It is best when medicating to have the help of a veterinary behaviorist if that is possible. It may not be, since there aren't too many veterinary behaviorists yet. It is sometimes necessary to medicate both cats, especially if the one being attacked develops nervous habits that further encourage attacks. It is often necessary to medicate for several months and then to gradually taper the medications to gain the desired effect. This does not work in a lot of cats, which is disheartening after a serious effort to resolve the problems.