Add testing repo
echo “deb http://YOUR_CLOSEST_MIRROR/debian/ wheezy main” > /etc/apt/sources.list.d/testing.list
Put
Package: *
Pin: release a=stable
Pin-priority: 900
Package: *
Pin: release a=testing
Pin-priority: 200
into /etc/apt/preferences
Update
apt-get update
Now install
apt-get install -t testing mono-complete