Had the exact same problem with Diamond - she's 2 but we've only had her for a few months.
In addition to what's been suggested above, I also tell her "okay, time for work!" then she goes to the flat place in the park where we work on her obedience skills (mainly "heeling").
She meekly goes over there, waits for me, I clip on her leash, we do a few minutes of obedience work and then I tell her "good work!!!" and we go home ...
She loves to "work", loves all of the positive reinforcement that goes along with it, and it sure makes the 'recall' training easier, because she knows that having her leash attached doesn't mean the fun is over!
Good luck ...