(Note that database changes might break your URD until you manually fix your database, so for normal usage, using the download link on this website or the 'export' method are recommended)
Keep an eye on the URD_db.sql; if that changes during an 'svn up' you probably have to update the database
run
svn diff -r ### URD_db.sql
where ### is the previous revision of urd you 'upped'.
You can check this with
svn info| grep "^Revision"
And it will print the number
So the correct sequence to run before updating through svn is
svn info| grep "^Revision"
svn up
svn diff -r ### URD_db.sq