The answer is that you typically don't lock files over NFS. Check out the Apache docs on NFS log files. They use a lock file on the local disk.

Some NFS implementations provide an okay locking capability, but I've never seen one that didn't fall down under heavy load. You might want to ask your vendor for info about your specific version.

You also could try using Samba instead. Joshua Chamas, author of Apache::ASP, reported getting better performance from Samba than NFS on his Linux system.