I read somewhere too that ticks hate cedar and some people put cedar wood chips around the perimator of their yard, you'd want it on the outside of your fence if possible though so your Yorkies won't eat it (I know mine would lol). Never tried it myself though.
I use Frontline Plus with great success and I've never had any side effect what so ever. Based on what I've learned, I think it's the safest one on the market. Honestly, I trust it more safety wise than anything that you would spray on the yard, even if it was "pet friendly". JMHO but my dogs constantly have their nose to the ground in the yard and occassionaly eat the grass, at least they're not eating the Frontline and I know for a fact that it's tested for safety on dogs. Anything you put on the grass is going to have chemicals too if it kills the fleas and ticks instead of just repeling them.
Idk, that's just my thought on it
