Here in Northern New Zealand I have had one cob and one pen mute (white ) swan from birth, the cob for six years and the pen for four. Neither can fly. From the day the pen was introduced to the resident cob he has taken a dislike to her. He chases her aggressively whenever possible and for hundreds of metres across country at a time. She has developed effective strategies against him and seldom allows him to actually catch her, she relies on me for protection when she can or she heads for my tractor and hides under it. She is very fond of the tractor and likes to be close to it when it is use. She also rests for hours beside it at the tractor shed. But she is very wary of the cob though not paraniocally fearful.
My expectation of these two DNZ-sexed birds is that they would breed but I have no answer to the male's aggression towards the pen.

My relationship with the male is that I am top dog and he is very respectful of this. To the pen I am a trusted friend. To each other they are anathema.

Have you ever heard of such a determined, year-round stand-off between swans of opposite sexes? if you owned them, what might you do ?

There is enough pond and pasture territory for any number of swans (five ponds and eight acres) it is just that HE won't accept HER.