Run thick beads of silicone on board, coinciding with strips on back of mirrors. Place first mirror on board and press into silicone. Repeat with second mirror. Apply silicone around edges of mirrors to seal.
Place dabs of silicone on edging in corners and in centre of sides. Place screen over mirrors and onto silicone. Wipe off excess silicone and leave to set.
To create split battens to hang mirror on, set power saw on 45° angle and fit fence attachment. Run down centre of 70 x 35mm treated pine, creating two battens each with an angle on one long edge.
Take one batten and use 45mm galvanised screws to attach centrally to backing board so uncut edge is flush with top of board. Make sure narrowest face of batten is against backing board. Also screw spacing block to bottom of board.
On fence, draw a level line 70mm down from where top of panel will be. Place second batten on fence so uncut edge meets level line. Make sure narrowest face of batten is sitting against fence. Screw through fence from other side (check with your neighbour first!) into batten using 30mm galvanised tek screws, going through every ridge of steel fence.
Paint battens and edges of backing board in acrylic paint to match fence. To hang, lift panel so batten on back hooks over batten on fence.