Here are a few strategies for finding and handling your competitors if they get to your website or in your lead database.
The best ways to find your competitors are form fill-outs and inferred data. You can use filters of these fields to find matching leads already in your lead database. Use the Data Value Changes trigger with these fields to catch these leads as they enter your system.
This is the best way to spot anonymous competitors visiting your web site. Try using the Inferred Company field to see if Marketo identified them by their IP address information.
There's a chance your competitors use their company email address when filling out your form. Search for the domains of your competitors using the Email Address filter with the "contains" operator.
Like email address, this is a straightforward way to catch your competitors as they enter their information in your forms.
You have a few choices for handling your competitors once you find them.
Changing these leads' Blacklisted flag to true will ensure that they don't receive any more emails from you. This is a good way to keep those leads in your database and ensure that they're not part of your email campaigns.
This campaign will spot those leads and blacklist them should they appear:
Deleting these leads was probably your first reaction, but you probably shouldn't. Instead, look at their Activity Log to find out what pages and offers they were viewing. Also if they return to your site, their subsequent activity will be added to that activity log (as opposed to added to a new, anonymous lead).