You have a couple options for smart lists here:
A) Use the Filled Out Form filter. If the form is being used in multiple places, click Add Constraint in the top-right of the filter and add the web page constraint. Assuming the munchkin tracking code on the page is working right, you can enter the URL of the page in that constraint. However, don't include the protocol (http:// or https://), just use the rest of the URL.
B) Just use a unique email address, one that isn't already in your database, when you fill out the form. Then search your Lead Database for that address. If the form is working, it should be there.
Grant, thank you for the help. I created a smart list and the form appears to working. My next question is: Marketo is not capturing the action of "Filled out form" in the lead activity log. Is this normal, as the webpage is not a Marketo generated landing page?
we have same question but it didn't work when i tried to use a url in the landing page constraint trigger field.
and i would like to know about the Filled out form capture in lead activity as well - that is critical for us.