I never had any problems with others getting into my casting zone. At times I had people stand behind me while flycasting but thats a different issue.
I have not let seen a person cast a boat rod far enough to interfere with my line anyway. With a half decent technique and correct weight it is possible to get good distance but most seem to have strangely balanced tackle. I quite often use boat rods while surfcasting. With them you can,t be tempted to cast towards the horizon. They are no good when the sea is big.