Placing the prop in close proximity to the keel seems to work to keep the prop from being fouled. I have a swing keel boat with a retractable spade rudder that draws less than 2 ft with everything up. Knowing that the owners would go in harm's way, the designer used a skeg to protect the prop in shallow water, but it also seems to be very effective in avoiding fouling from lobster and crab pot lines.
We sailed the boat home to Mystic from Clearwater Beach, FL. That trip was about 1700 miles and included the Chesapeake. We've since been to Maine twice, where it can be a challenge to avoid the lobster gear and we also have lobster pots in local waters. In the 17 years I've owned SeaScape, we've never snagged a line on the prop.
When we were having the boat commissioned in FL, I inquired about Spurs, but the yard manager told me I'd be wasting my money because of the skeg design. He was right.
That said, my experience verifies the claim that the typical full keeler would likely have next to zero problems with lines fouling the prop.
BTW, should I hit anything hard with my 3000 lb swing keel, which is fully retracted here, there would be some damage to the leading edge, but it would kick up to mitigate any other damage. (We could get into a whole other discussion on this category of keel!)