When I got my Rottie as a pup, I signed up for insurance right away and paid on it for about a year. When he was diagnosed with hip dysplasia, I found out what all the 'fine print' meant.
It didn't cover a penny; not even for the diagnostic Xrays. I would have been better off putting the $40.00 a month or whatever it was in a savings account as well as budgeting a little extra; like you do for a kid and a college education. IMO, Pet Insurance is worthless. The insurance companies make certain they know all the breed predispositions and 'insure', you are not covered. Unless you feel your dog is at a high risk for getting hit by a car or exposed to an accidental injury, then yes get insurance.
BTW, I'm usually not this cynical; I have auto, homeowners and medical insurance coverage. My suggestion is setup a savings account you can 'insure' you will only access for the dog. That's my plan next time around.