In regards to the Jump Rock - yes, please remove the fence and try making it safer.
Instead of your suggestion of requiring an app to check the tide, how about simply adding a red-amber-green "tide marker" sign and/or paint on the rock face, so that when the red shows (i.e. the red colour is not submerged) it's too shallow to jump, and if only the green is visible it is ok. Or something along those lines.