I like to use what I call "tactic programs" that help associate ad spend with specific calls-to-action. For example, I may have an upcoming event, for which I have a Marketo program, but I'll also have a related program that associates people who sign up for the event having come from a LinkedIn ad. I'll associate all related LinkedIn spend with that program.
It ends up looking something like this:
FILLS OUT FORM > Form is EVENT REGISTRATION > Web Page is UPCOMING EVENT > Querystring contains "src=linkedinad"
I'll have a flow step setup behind that trigger to associate those people with that tactic program, so I can always go back and see how many people were driven to sign up for this event from a LinkedIn ad. The nice thing is, I can event eventually associate revenue with those LinkedIn-sourced registrations via the SFDC Campaign sync.