I'm so sorry to hear about you and Rusty! I can feel the frustration and worry over the internet!
First, yes, you can give him a valium along with the acepromazine that he already got, and the melatonin.
I'm not sure where you read that ace isn't good for stressed out dogs. It isn't an anti-anxiety medication, but a sedative. In aggressive dogs it can cause them to be more aggressive, but that doesn't hold true with stress.
Here is a website with good info about ace: http://www.VeterinaryPartner.com/Content.plx?P=A&A=570
Does Rusty have any problems with stiffness or pain? I would ask your vet about prescribing tramadol to try at night. Tramadol is a pain medication that is also sedating, so Rusty might sleep better and feel better overall.
Thank you. I very much appreciate you getting back to me. I have read several articles recently about Acepromazine being a great sedative. It has always worked on Rusty when he would need to be sedated for an x-ray or an ultrasound. He was happy go lucky then; never exhibiting signs of any kind of anxiety. His old age seems to have brought the anxiety out. The articles claim that the Ace can, in fact exacerbate fear....nonetheless I will keep trying. I will try a valium tonight. Is 5 mg. a good dose for him? He is about 70 lbs.
If that is what your vet prescribed for him. It is a rather low dose, but may be sufficient in conjunction with the ace and his age.