Re leaving your boat on the beach during a symposium or other event.
Jim and I never did so when we were at an event, and I don’t recall ever being at a symposium where that was a common habit. The boats went back onto the roof of a car at day’s end, either ours or someone else’s if were had combined boats to reduce parking issues at a launch area. The closest it came was one symposium where people could leave them on the lawn in the back yard of one of the organizers rather than haul them back to their rented space. Many years ago at the Castine Maritime Academy a few privately owned boats were left with the rentals for coaches to use, but that was only as needed. My recollection is that people were holding their breath for the brave soul who left his own boat for Wayne Horodowitch at Castine. He is a very big guy and had a reputation for using boats hard.
I have seen photos that have a lot of boats on the beach at some of the southern events, but that may not have been the case overnight. Personally, the most risk I would take would be to leave my boat on the beach long enough to grab a car pool ride back to my room and return to pick it up. I would not leave it overnight because it represents such an obvious target. Let them steal some outfitter’s rentals or demos instead.
A lot of it comes down to location. Here in the frozen north I have never bothered to lock my sea kayaks that are under the rear deck. But I live in a city and over the years Jim and I encountered enough of our neighbors to know that as much as they may admire the boats or the activity, most people are not remotely equipped to do anything with 17 feet of a kayak . One night we heard some of our shakier neighbors talking about the boats over a barbecue in the back yard. All of them agreed that they wouldn’t even think about getting into one of our sea kayaks because they “would die”. We liked that - scary boats are a good thing. I do lock the ultralight canoe when it is out - it weighs nothing and people aren’t so scared of canoes.
But for trips to Maine in paddling season, I am going to a area of obvious opportunity. So I travel with lasso locks, five straps per boat (two at each of the normal points even on the Hullivator side and one in the middle) and bow/stern line as needed. For the last, how many individual lines varies by length of drive since having a strap right in your face is more annoying over a 7 hour drive than one hour. I would do the same thing heading south. Not that a boat couldn’t be taken by someone with time and a decent wire cutter, but it’d take them so long they would likely look elsewhere. In a hotel, you could even find a motion-activated beeper of some kind to hide in the boat.
Locking a boat to a tree is only effective if there is a metal cleat on the boat to lock to, doesn’t take much to cut a perimeter line. If camping, probably best place would be right next to the tent.
I never left much stuff in the boat at symposiums because they were all at the ocean, and mold could start overnight if things were not aired out. Theft of the items never really entered the picture because of where I was paddling.
Hotels are a different risk, as above. Jim and I did that occasionally, but it was never a really commercial type place. More like cottage settings. In a Holiday Inn type place, I like the idea of putting a motion sensor in the boat that would scream, or just loading the cockpit with a bunch of loose cans that make noise.