cockers are very intelligent dogs and if they want to get someone very little will stop them (Taz has found his way out of at least 3 "fully enclosed gardens"

we had a stairgate when he was a pup, took him about a week to work out how to open the gate (standing on it to push it under the clip), so when i had to nip out for 20 minutes once, i wrapped an old collar around the gate and the stair bannister so that it wouldnt open. Imagine my surprise when i returned home to find both dogs upstairs with the collar chewed through - it had took him less than 20 mins to work out what was stopping the gate opening and doing something about it

I think it is just persistence with the cat. I have got mine to the stage now that if she sits still they leave her alone, but if she runs then still chase. Lots of treats when they leave her alone as worked best.