Why can not a good reference from the first job be sufficient guarantee for the second? (lawyer-monthly.com)
God's Word is not sufficient guarantee, we want something more certain. (religion-online.org)
Milner is a hugely experienced campigner who is apparently pushing for regular action in a central midfield role and van Gaal may well be ready to offer the Man City man sufficient guarantees in that department. (caughtoffside.com)