Does she hate to be buckled?
For us what works (still) is that we have a deal. Joy doesn't try to escape, I don't buckle her. If she DOES try to escape, she gets buckled. When she was younger (under and around one year) that also included standing up in the stroller.
At two your DD is old enough to understand that correlation. "If I try to run, mommy buckles me. I don't like being buckled." It may take a little while, but it does work. You just have to reinforce the lesson consistantly.
The next time you go out, tell her, "I won't buckle you now but if you get out of the stroller you will have to be buckled." And follow through. The very first time she tries to get out (and she WILL - that's part of being two!), buckle her up and (without any recrimination or lecturing or anything, just a statement of fact) say to her "You climbed out. Now you must be buckled. We'll try again next time." And then next time, try again. Next time can even be on the same trip if you have reason to get her out of the stroller at any point.
It works very well for us. Joy *
hates* being buckled in the stroller, and I'm not willing to chase three kids.
:twocents: