We have 1 old small Toypom female, 1 female cat and two 4-year-old Great Danes, a male and female (brother and sister), both sterilised and healthy with lots of open space to run. All the above animals behave well except for the Great Dane female. She does not listen to us at all, no matter what discipline/reward system we use. She would force her way into the kitchen pulling food off the counter tops, throw the dustbin over to find food inside. The animals always get enough food and water on a regular basis but she will always go eat the small animals food and water. On a few occasions she tried to bite the Toypom female... and in general just keep pushing her luck, when reprimanded she just wait 5minutes and go do the same stuff behind our backs. Today we took the Toypom for a grooming, when she got back home the female Dane sniffed her constantly while wagging her tale and we thought all was okay, and then 20minutes later she almost killed the Toypom, thats when I lost control and smacked the female Dane hard with my hands and order her into the house - I feel very bad about this, spur of the moment... Please give us some advice.