Do coastal weapons create true naval no-go zones?

Would coastal defenses and missiles create no-go zones for fleets?

Not absolutely; they raise the level of force and suppression required to enter, which may make another route more attractive.

A maritime no-go zone is too absolute a description. Missile batteries, mines, guns, and airfields make a fleet bring carriers, escorts, and suppression assets before entering, but they do not create an inviolable barrier. A commander may still choose a weaker approach, as Allied planners chose Normandy over the most heavily defended part of the French coast. The useful concept is an entry-cost threshold: coastal defense can make an operation impractical without making it physically impossible.