svnsync - couldn't get lock on destination repos

Actually, there is some functionality built into svnsync (since v1.7) that can "steal" the lock.

svnsync help sync

shows:

--steal-lock             : Steal locks as necessary.  Use, with caution,
                           if your mirror repository contains stale locks
                           and is not being concurrently accessed by another
                           svnsync instance.

and when I run it, I get a nice:

Stole lock previously held by '[hostname]'

So, you don't need the propdel thing after all

You have to remove the lock property on the remote repository via svn command line on the remote site which has been left over from a failure during synchronization.

svn propdel --revprop -r0 svn:sync-lock file:///path/to/the/repository

Technically, it is the destination repository that you need to delete the property from, not necessarily the remote repository, as the destination could be local. So for this specific question:

svn propdel --revprop -r0 svn:sync-lock ${REPO}