Trying to wrap my brain around a routing question.

I have two sites.

Both sites have their own internet (redundant internet in fact).

Both sites have FW clusters on their egress.

Each site is also connected to the other over a double-redundant L1 dedicated fiber on the inside with diverse pathing. Cuts on one path do not effect the other, I incur no noticeable outage in that event.

Each site has a default-gw to egress out it's local internet connection.

My question is this:

How would I maintain local internet-egress at each site, while also auto-failing a site to the others internet in the event of an outage?

Most of the options I can think of end up favoring one site or the other. I do peer BGP out both sites internet connections, I'm no where near strong enough in BGP to try to do anything fancy with it internally.

My other possible option is to setup SLAs on my cores, pinging out to (maybe) my bgp peers, and then rewriting my default route on the internal cores to flip it to the other site in the event that both ISPs shit the bed.

In case anyone is wondering how likely it is this would happen, I'm about 150 yards from the surf in hurricane central. My Dr site is currently 60 miles inland.

Thanks for the responses in advance.