They were also told that they should have had a flag pole on the top
In some harbour areas etc there may be a bylaw to this effect. Anywhere else it would certainly be good practice. We all know how annoying a rope round the prop is. On a sailing boat where you can't just tilt the drive leg up its even worse. Ideally you'd have some reflective tape on it too. If your rope does get struck expect it to get cut in which case you will loose the pot and the buoy. I use a flag from a children's trailer bike that i have improvised into a 'dan buoy'. It makes it much easier to spot the buoy when going to retrieve it too.
I've only ever caught crab (and a lot of star fish!), I was told crab prefer 'older' bait and lobster prefer 'fresh' - not tested to see if that is true.
If you do loose the pot for any reason (bad knot, cut rope, big storm etc) then the trap will continue to work attracting more and more species to eat each other. That's obviously not very good - so I believe they should be made so that part of the pot rots away if left continuously in the water for a few weeks.