I use the 4' loop camstraps from DRE (they're actually two straps, both with small loops at one end, one strap has a buckle, they're used for holding in the cooler or drybox). One strap is attached to a steel ring on the oar and the other on the boat is looped around the frame next to the oar tower. I can take them off by undoing the camlock & I haven't lost an oar, yet. It seems to work well though it may not have a weak link (the buckle, maybe?) like Diesel mentioned.
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse