Any way to track who has been executing what queries? who has been on my lawn?
Queries aren't logged by SQL Server, unless they meet some criteria that puts them into the default trace or system_health Extended Events session (some details on what they collect here). 

If you can control data access via stored procedures, you can easily add your own logging to those. But that doesn't sound like the case. Otherwise you will have to rely on triggers (for DML, but not SELECT), server-side trace, extended events, auditing, or 3rd party monitoring tools.