Capturing UTM values

Hi,

We are looking to capture the last visited UTM values from the referral URL that brought the lead into the system. Is hidden fields (in a form) capturing the value from the URL the only way possible? Any other alternatives to do this? And can we efficiently do this for an old lead in our system who re-engages with us by filling out another form. For the old lead we would like to capture the last UTM values that brought him back into the system.