COWS!!!

We have for several years had intermittent problems with the invasion of the "Ninja Cows" and they are back again. They munch and pull up everything, push over fences, churn up the ground and worst of all they poo everywhere! It's all over the place , you can't escape it when walking, my shoes are now cow pat coloured, the dog is cow pat coloured and the final indignity after I slipped and fell, my jeans are now cow pat coloured too.
I call them Ninja Cows as this phrase was coined by my shaken up Hubby after he encountered them unexpectedly a couple of years ago in our garden at night.....he had taken the wonderful Blue out for a wee before bedtime and they went to the top of our steeply sloped garden via the steps. Blue was doing his thing and Andy turned around to find himself eye to eye with what he describes as an 8ft black cow (I feel that fear magnified the beast)  that had appeared from nowhere. Screams and yelps followed as man and dog dashed for the door, squashing past each other in their desperate race for sanctuary. When he could make coherent sentences again,  he insisted that the cows had come from nowhere and from then on referred to them as Ninja Cows.
Following this incident a few weeks later I looked out of the kitchen window to see 8 or 9 of the bloody creatures ravaging the garden, I flew out with stick in hand shouting like a wrangler but to my utter dismay I was treated with complete disdain by the cows. They looked up from their chewing briefly eyed me up and resumed said chomping. I couldn't get them out of the garden no matter what I tried. In desperation I telephoned the local constabulary for some advice. The very nice policeman on the end of the 'phone asked me what the trouble was and I told him, I asked him if as they were trespassing on my property could I shoot them? (I was very angry and desperate at this point). He didn't know and went to ask further advice, he returned to say that partial as he was to a nice bit of steak I cannot shoot them without a specific license to do so. He did however say that I could phone the local authority and they would come and collect them.
I called the council who duly sent someone out to round them up but they had gone...not just wandered off a little way, the Ninja Cows had completely disappeared, nowhere on the lane were they to be seen and the council men left obviously thinking I was hallucinating or barking mad.