When dogs become obsessed or fixated with things, it usually means that they are either not getting enough physical or mental exercise or they are insecure. The obsessive activity becomes a way in which a dog releases the stored up energy it has. There are certain dog breeds that require mental stimulation just as much as physical exercise because they are so intelligent and in some cases have working breed instincts.
I have two working breeds in my pack- Freddy, Jack Russell and Alfie, Springer Spaniel. They both thrive on activities like dog agility or search and find games and if they don’t get that fulfillment regularly they start to exhibit unbalanced behaviour, particularly Freddy who starts tail chasing!