Marty Duffy (Sligo) THE Sligo whistler can be a bit pernickety at times, and both sets of players will be well aware of his sometimes over-zealous style. But Duffy's not the worst on the circuit. He will be well aware of the difficulties Derry ref Barry Cassidy had when the two sides met in a Division Three match in February. Cassidy was forced to brandish five red cards (Three for Monaghan and two for Cavan). So Duffy will be keen to clamp down early on any niggly indiscretions.