OK, I get it.  I need to reference the forms object, like

Me!Obs_Site_ID

It's surprising how far I've gotten on minimal learning.

It's difficult to help without being able to see it. Maybe some screen shots? Text descriptions only go so far. Also, try not to have a field named "date". That will cause problems. Unless you mean Date() the function that returns today's date.

I apologize for being brief.   My 'date' field is actually named Obs_Date.   I had trouble formatting my search string correctly to accommodate a date field (had to surround with #....#) and a text field (had to put in single quotes).  I will be more clear in the future.   I have it working now.   I use both methods together - I use the Access composite unique key to positively prevent duplicates, and the VBA code on the form BeforeUpdate event - together they catch duplicates both on additions of new records, and updates to existing records.   Thanks.  

Not clear how to insert screen shots in a comment.

My site isn't as fancy as some other ones like Facebook, so you can't put a screenshot in while you're typing in the text. But after you submit your text, I see in the bottom right corner it says "Upload Image," or at the top of the thread you'll find a link too.

I thought about adding the capability to just paste photos right into the text, but it requires a lot; it's JavaScript and back-end processing, and it's just a nightmare. What I've got now works, so I'm sticking with it until I've got a lot more time on my hands to be able to upgrade the site to that level of complexity. LOL Access is easy for me; JavaScript, not so much.

But yes, it's much easier to help you if we can see what you're dealing with instead of just what you're describing.