Well don't we know about this, lots of dogs escape and there are various reasons for it, the most common one that Ive had to fix is separation anxiety. Staffies, Huskies, Malamutes seem to be the most prone breeds to suffer from anxiety and escaping.
You need to make sure your boundaries are secure first before you even begin to work on escaping and anxiety. Even little puppies can suffer from this, so you need to get your fencing etc. really secure and then see where you are at.