So I have a dog in my house and I let it outside and it all of the sudden went for my rabbit and almost killed it. This has never happened before when I put my dog outside with my rabbit. What should I do to help my dog to never do this again? I also let my dog out everyday for the day and I feed him enough so there can't be any sign of him being hungry. Also he has access to the house from the outside.
I don't really have enough detail to be precise, but generally speaking - dogs have a chase instinct built in. By any chance was your rabbit running when the dog went after it? It's not uncommon for dogs to ignore an animal until it runs, and then be quite excited afterwards.
The problem is - when they 'catch' it, they do so by grabbing it with their mouth - and that potentially means they'll kill a small fluffy animal when they do.
We've had our dog chase a chicken, catch it, but then be unsure what to do with it, and proceed to lick it's head.
I'm afraid chasing things is a difficult habit to break in dogs - because they enjoy it, it self reinforces every time they do it. The way to train it out is introduce an incompatible behaviour, and reinforce that.
For example - training your dog to sit instead of chase. You will need to watch for, or encourage the 'trigger' to the chase instinct, and when they do... make them sit, reward with a high value* treat and encourage them to pay attention to you instead.
You will need to do this repeatedly, and be very careful whilst you do - your dog as learned that rabbit chasing is fun, and will do it again. And if they have fun next time, they will do it again and that will become increasingly hard a habit to break. I would suggest you don't let your dog off lead near your rabbit until you're happy that the retraining has properly sunk in. (And even then, you need to accept that there's a degree of 'natural predators' going on here - some dogs will never be entirely safe around things like rabbits).
* Dogs have certain things they like more than others. When training, particularly with things that are also demanding their attention, you need a treat that they'll be particularly obsessed about getting. Ours really likes tripe sticks, bits of liver, small pieces of cheese. As far as we can tell, the stinkier and messier the better.