Hello Ramsby! I am sorry that you loss your Cham.
Could you do us a favor and please take pictures of the cage and setup you have been keeping your Chameleons in. Also, please state the location of the cage currently. Since you say you are thinking of making a Chameleon Room.
You say it was your sisters dog who has done this. What steps has your sister taken in correcting this behavior? She is just as responsible for the dogs actions as the dog is.
May we ask how old you are? Sometimes people just aren't ready for a Chameleon yet since it takes a lot of responsibility, patience, love, and respect for the Chameleon.
As others have mentioned. If you are able to keep the door closed while handling your Chameleons then do so. I have two dogs that are both over 120lbs each and are taller than I am if they stood on their hind legs, so are quite capable of hurting one of my Chameleons if they wanted. However, they know if they were to touch my Chameleons I would scold them, and hurt them in return. I'm not saying you should hurt your sisters dog, but I'm saying each owner corrects behaviors that are inappropriate and have different ways of doing so.
Also, how often do you tend to take your Chameleons out of their cage? Most tend to want to be in their cage and not handled 9/10th of the time.
Have you ever owned another reptile? If not, maybe you should try owning a Leopard Gecko or Bearded Dragon. They are a bit hardier and don't stress as easily as Chameleons.