Excel - allow duplicate entries into a table; however, restrict to only one entry per day

[jhedges]

I'm trying to allow multiple entries for a person into a table and restrict one entry per date. So, there could be multiple entries for person X, but only one per day. I have found numerous ways to validate data with conditional formatting and VBA and I'm not opposed to use either; however, have not found a specific example to my problem. Anyone have any ideas?