I have a spaniel with OCD, she is obsessed with the fish in my pond at the bottom of the garden. This dates back a couple of years ago when she would come fishing with me, we were in North Wales and staying in a little cottage by a lough. There were no trout in the lough but I was happily catching small perch using nymphs. The dog would always sit beside me and watch me fish, it was a very contented scene. I was in the process of landing one of the little perch, had the fish on the surface and reached down for the landing net when the fish splashed and got off. The dog gave me 'that look' you know the one that they give you when you miss a cracking bird or rabbit, as if to say 'what did you let that go for?'
Anyway the next fish I caught a bit later, there I was bringing it in to land again when the dog obviously thought 'you're useless at this' and jumped in to retrieve the perch, hook line and all! The fish was delivered to hand and unharmed and quickly returned to the water, which the dog was not impressed with! I no longer take her fishing as she is now completely obsessed with water and fish.
If left to her own devices she would spend hours just staring at the fish in the pond. If we go anywhere with water she'll stare into the water in hope of seeing a fish or even cathcing one, she has on occasion even fallen in! I think it's the fact that she can see the movement of the fish but there is no sent to pick up on, it is funny if not a bit tiresome at times.
Anyway, not much help to you and your problem, but your not alone in having a dog with OCD. I think with spaniels it is very much in their nature to become obsessed over things. If they wern't obsessed with hunting they would'nt be much good!!!