If you don't have a hypercracker, or just don't fancy the strain it puts on your drop out, try using a removed chain to hold the cassette still while you undo the lock ring.
Wrap a rag around the chain where you hold it, and around the tyre so it doesn't cut into it and cause damage. Then get a helper to use a standard lock ring tool and a suitable long spanner to release the lock ring.
Worked for me!
Home Equipment index