I've bread bulldogs for a couple of years now and owned many other dogs, I suggest get a spray bottle and put some citronella (sorry about spelling) diluted with water in it, strong enough so it smells bad but not to strong to sting there eye's etc. Go out in the yard with a plasitc lizard you could use a real one but you don't wont to take the chance, anyway tie a peice of string on the lizard and get her out there with it and pull it along as if it was real so to grab her attention, make the string long enough though that your not standing right beside it and it dosn't look as if your the one moveing it, even if you can get someone else to do this it will be a bit easier, everytime she goes for the lizard spray her preferably around the mouth and nose area with the mixutre in the spray bottle, she will hate it and the smell will stay on her nose for a while, if she continue's to do it continue to spray, also use a deep cranky voice at the same time and say Bad girl or boy whichever it may be, this may sound strange but does works, dogs arn't stupid and they soon will realise why there getting that yucky stuff in there face, it's not going to permenatly stop her just after one go so do it a couple of days for a couple of weeks until when you do take the lizard out she'll leave it alone. At the end of the day dogs are curious critters and like to chase things that move around and look threatning, all you can do is teach her it's not accepted.