I have a few suggestions:
1. Create a campaign for your remarketing efforts and tie them to any landing pages you’re using. You’ll be able to see how many contacts were “influenced” by the campaign and the number of deals closed that were influenced by the campaign. How to set up campaign analytics.
2. Create a “Campaign Code” property and create a workflow that assigns that code to anyone who fills out a form on the pages that includes your UTM parameters.
I hope this helps!