"constant protection" is correct and can be used in written English.
Example sentence: The security system ensures constant protection for our home.
She's under constant protection by bodyguards, and she rarely parties.
... Specially trained agents from the Justice Department's F.B.I. provide constant protection for Sessions and [James Comey].
But it is easy to name many officials with far more constant protection.
Freedom of speech requires constant protection; all governments hide information if they can get away with it.
Many schools in the city have no trouble with safety, and both girls will be under the constant protection of the secret service, not the local custodian.
We've had it with your constant protection of your Democrat overlords, your refusal to acknowledge any truth that upsets the fragile construct that you believe is real life.
Since this incident Wilders has been under constant security protection because of frequent threats to his life.
Since then he has received numerous death threats and has lived under constant police protection.
Ferguson's relationship with Hirsi Ali is further complicated by the fact that she lives under constant police protection.
A Republican and close ally of Mayor Rudolph W. Giuliani, Mr. Molinari has had constant police protection since 1995.
Mr. Wilders, who lives under constant police protection in an undisclosed location, is undeterred by threats from the Taliban to escalate attacks against Dutch soldiers in Afghanistan if the film is released.
