Leaves – Thoroughly blow off as much leaves as possible; any leaves that get trapped inside the ice will cause havoc as it will draw heat from the sun and melt the surrounding ice. This happens even to leaves that are trapped 5 inches below the ice surface
Uneven ground – creates gaps around support frames, putting parts of the plastic sheeting in extreme stress, possibly resulting in leaks from small rips;
Initial freezing of water – Think layers. It is far more durable to have multiple layers of ice frozen at different times. You can also remove leaves and other contaminants and fill it back with ice. Can’t do that once the leave gets trapped below 5 inches of ice.
Good sites to learn about building a backyard ice rink