I've rescued a small dog which was weak, skinny and shy. The new dog enjoyed having time with my energetic female dog and they played well, so i let them run together. A few days later, something changed. She jumped over him and a stair accident occurred. Although he wasn't hurt physically, since then he's been scary of my dog. Even worse, my dog has kept jumping over the new dog, chasing him whenever we go for a walk, biting him for fun, stopping him to eat and stealing his food. I've isolated them when i'm not home and given them different bowls for water and food. When he's bullied, i always say 'no' to my female dog and stop her, but nothing helps the new dog to remove his fear on my dog. How should i deal with this?