All you need do is say you what you want it to mean - no legalese needed and make it clear:-

"A maximum of one week's leave only can be taken between X and D. All other leave must be taken between X & J. " Or whatever you need it to say. You can of course put caveats in such as:" The only exceptions are for the following reasons:-......." However, you then leave yourself open to people who may not be telling the truth. You could also say, "No leave outside these dates will be allowed unless approved in writing by the CEO, Manager, Kitchen cook, cleaner etc., :-)

And just to make sure take it to someone whose English is good and ask them to pick holes in - if they can't then its probably clear enough.

If you're updating an existing A/L policy do cross reference your contractual clauses first (ie what your ts & cs of employment say about A/L) so that your policy doesn't inadvertently contradict the ts & cs. out of interest, why does your organisation want to mandate when leave can be taken - is it due to certain times of the year needing 100% of workforce in? Bear in mind that annual leave booking should always be by mutual agreement (ie managers can reject A/L requests if they have good reason) so you may want to consider how restrictive you want your policy to be, or whether you make it clear that there will be times of the year where taking annual leave will be limited etc etc, that requests won't be unreasonably refused, but operational requirements will be the deciding factor in any decision to accept/reject a leave request.