Many publishers are open to you retaining some rights. Adding an addendum to your contract/author's agreement with your publisher is a convenient way to seek the rights you would like to retain. Here are the steps to attaching an addendum:
If you need to secure the right to deposit your article in NIH’s PubMed Central, NIH suggests inserting the following language into the publisher’s agreement:
“Journal acknowledges that Author retains the right to provide a copy of the final manuscript to NIH, upon acceptance for Journal publication or thereafter, for public archiving in PubMed Central as soon as possible after publication by Journal.”
For more information, visit the NIH Public Access Policy LibGuide.