"remain guarded" is correct and usable in written English.
You can use it when you want to express a sentiment of caution, to remain alert and not trust someone or something too easily. For example: "I remained guarded when the unfamiliar person made me an offer; I wanted to make sure I wasn't being taken advantage of."
In what ways do you remain guarded?
While we welcome today's announcement, we would remain guarded till the bill for a separate statehood for Telangana is passed by the Indian Parliament," Mr. Rao added.
But some conservative Christian leaders, even as they say they will of course vote for the Republican candidate, remain guarded about Mr. Romney.
McConnell's recounting of Catherine's attempt to start her life anew is smooth and self-assured, but the characters remain guarded and at some level impenetrable, as if they were being protected by the Secret Service personnel who populate these pages.
While Leicester remain guarded about the potential candidates, the Premier League club insist Sam Allardyce has not been approached and that no deadline is being put on the time it takes to bring in a new manager.
Therefore people remain guarded, to ensure that they do not show themselves to others in an unfavorable light.
These interventions remain closely guarded secrets within the establishment.
What Messrs. Corzine, Schwarzenegger and Bloomberg do on their many private trips usually remain closely guarded secrets.
And Brad Pitt and Angelina Jolie, who made $50 million between them by the Forbes count (which tries to best assess what remain closely guarded numbers), have a home in Louisiana, where the tax rate is 6 percent.
Though details about the new zone, almost four months before this year's event, remain closely guarded, Debs Armstrong, one of the area's creative directors, said it would contain "all the wonderful world of things that you can do when you don't have to do burlesque any more".
Malia's grades and standardized test scores remain closely guarded secrets, but factors in her favor in gaining admission to Harvard included her family background, study at top-flight schools and a unique upbringing that was bound to make for a remarkable college essay.
