Non Competes rarely hold unless proprietary property is used/stolen..ie intellectual property, tradesecrets, copyrights etc.. I would have them sign one anyway as a deterrent.
Many professions face this problem, law firms, accountant, ad agencies, realtors, investment advisory and more. Often these companies spend 10's of thousand developing talent and that talent leaves and strikes out on their own AND more often than not, will take valuable clients with them. And you can't do a fucking thing about it.
So I wouldn't worry too much about it, the worse thing that could happen is you teach someone a new skill and they steal a campaign or two and go it alone. I'm telling you though, if their paid well, treated with respect, and ur not an asshole 90% would rather just stay than go on ther own.
btw.. My most loyal employees have been young married mothers that have husbands with decent jobs.
[decent jobs]=really long hours and are never home and young wife feels neglected and horny....ftw
I love casual Fridays