If you don't want them to fill out the form at all, you'll need some javascript to preven that.
If your situation means you're sending out an email after the fill out (or registering, etc), then why not do this:
Register Campaign Flow:
Smart List NOT IN Competitors
Make sure you have that competitors smart list that looks at Company, Domain, Email, etc...to
Then the system blocks any competitors from being put through the flow. Their data is in there, but they don't get the email or content. They'll never be sure what happened, then you can monitor their activity.