Number RSVP cardS and log who has which number on a spreadsheet. Easiest way to track who still owes you an RSVP. When you don't get them back (and there will be many that you won't, its just how it goes) you know exactly who to confirm with.
Look it even has our initials already! Rustic Wedding Chic - Rustic Country Weddings - Rustic Wedding Ideas and Venue Guide. Love the mums and letters idea with the reception sign. Diff colors for letter.