Mumford impressed in the reserves but was offered a contract closer to home with Swansea City. Mumford started his career well at the Vetch in both defence and midfield.
In the last year his time has become sour, failing to start a single game last season for the Swans. Instead spending time on loan with Aldershot for a month.
The 23-year-old needs a kick start to his career and will be hoping that comes at Blundell Park.
A powerful and pacy forward, Holland recently netted a hat-trick against a full strength Sheffield United team in pre-season.
At the moment he is subject of much talk of a transfer to Hucknall Town but Margate are remaining coy on the issue. Seemingly Holland is waiting to see if he can earn a contract with Town before making any decision on Hucknall.