Pug refuses to walk unless round same area of park

I take my 9 year pug for a walk three times a day, l.have a great Park big enough for him to walk round once one minute away from my house. But the last couple of years he seems like he’s so bored walking round it. He will start off walking quite happily doing his business then he stops and sometimes refuses to move, it’s like he’s realised that he’s in the boring park again! I try taking him different ways around the park and streets but still the same, but if we start to go in a different direction he suddenly speeds up so l know there is nothing wrong with his health. He has a slight slipping knee cap but as l say if we go somewhere he doesn’t usually walk he speeds up so l don’t think it’s that, maybe he’s just getting stubborn in his old age!