easiest and most effective way (in my experience):

1. after your lock ring is off, put the wheel back in the bike, and put the chain back on
2. sit on the bike and pedal backwards
3. if that doesn't work, stomp on the pedal in order to turn the chain.

this has worked for me when everything else has failed.

edit: and if that fails, go for a ride without your lockring, and try to skid (with brakes I hope)