They make propane cannons that go off periodicaly, they are used to protect crops from birds. My uncle uses one in his 4.5 acres of grapes and it does a good job at keeping the birds out, I don't think it works on Racoons. Have your tried noise makers? or a radio? Also state governments are stepping in in some places to control cormrants, maybe they could help?
Don't shoot cormrants yourself, big time fines.
