HTML editor is incorrectly encoding an & in my code

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Via the HTML editor I'm entering something like the following:

<a href="http://myurlishere.com?cp=careersite&d=http%3A%2F%2Fanotherwebsite.com%2Fsearch-and-apply%2Fapply-here">

my problem is that the editor kindly corrects my ampersand here:

careersite&d=http

to this:

careersite&d=http

which breaks my URL.

How can I edit a page without having to suffer the editor?