WA Big Cats

My second big cat sighting was in  Kemerton a few years later. We were coming  back from Australind from crabbing  driving along Kemerton road heading  towards the South West HWY. It was  summer so it was still daylight at 6pm.
 We were driving through dairy country  so we had open paddocks either side of  us. I remember coming around a corner  and seeing what I thought was a Black  Labrador walking along the top of an  irrigation channel. In my car was my  sister and my girlfriend (in front  seat) I said her thats an odd place to  see a dog. My girlfriend who was a vet assistant and animal lover went pale  and said thats no dog. I immediately  pulled up and we watched this thing  (not bothered by us) walk "slink" cat  like. All 3 of us said do you see this  too? Next second my mate (who worked  for the APB) came to a screeching holt  behind us, jump out of his car loading  his gun but this noise had startled  the big black cat and it ran of out of  view across the paddock. All of us  agreed that what we had seen was a very  large black "panther"? cat. My  girlfriend shaking kept saying over and  over "dogs do not run like that"