There are several synonyms for the phrase "keeps out," which means to prevent entry or access. One of the most common synonyms is "exclude," which implies actively preventing something or someone from entering. Another option is "prohibit," which suggests a more official or regulatory restriction. "Bar" or "block" are more forceful synonyms that suggest physical obstruction. "Deny" or "refuse entry" are more polite alternatives that may be used in formal or professional settings. Finally, "repel" or "ward off" suggest a more defensive strategy of actively avoiding or resisting entry.