Actually, there is a boundary cable in place demarking the restricted zone. It runs more than 1000 feet, from Cove 2 to Cove 3 ... strung between cinder blocks in a manner very similar to the Edmonds trails.
We have tried different approaches to making this cable more visible to divers. The first involved pool floats attached to strings ... that floated about 3-feet off the bottom. They were quite visible. Unfortunately, they also proved to be entanglement hazards because of the amount of diver traffic using the boundary cable as a rope trail (not its intended purpose).
So last year we removed the floats and attached about 200 1-gallon orange juice jugs, zip-tied directly to the boundary cable in an attempt to make it more visible (and float it up off the bottom a bit).
We installed two additional rope trails southeast of the boundary ... one leading to the I-beams and another to the Honey Bear. These are the two most popular attractions in the park, and we figured if we made it easier for people to navigate to these locations, it would encourage them to not plan their dives around the boundary cable. To a degree, this approach was successful.
However, due to the amount of structure alongside ... and just inside of ... the boundary cable, there are still those who think they can break the rules just a little bit and not cause problems. All too often though, once inside the restricted area they get turned around and end up underneath the fishing pier or water taxi berth.
BTW - Edmonds has had several incidents this year involving divers near ... or under ... the ferry terminal. They have also instituted a "no tolerance" policy of fines for divers who are caught in the restricted area. I think the fine is $500 ... and divers have been cited. That's a powerful incentive to not go in there. We have been trying hard not to impose this kind of "incentive" at Alki ... but that might end up being what it takes.
... Bob (Grateful Diver)