How big is "a big dog" to you? I know different people have different ideas on the matter, so that'd help I think.
Also, is a puppy an option? A dog that will grow up with your kids will just make him/her that bit more special to them when they're a bit older (I dont know why, but I'm assuming you have young children  ).
It'd also mean you get to train the pup your way, with your words/commands and so on
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