I want import a list & isolate it so that it does NOT sync to Dynamics CRM? Any ideas?

We are going to use a list for Recruiting purposes and therefore do NOT want it to sync to CRM. We want to keep all of our Sales leads safe. Any ideas? Static list? The # of people on the list (that we have yet to import) is 900. Our Marketo expert told us to do a test list of 100 and run that through to see what happens before adding rest of list. Thank you!