I've never had a pitbull type dog or any big dog fail to stop within a respectable parameter when the umbrella whooshes open before them and the defensive, heavy duty version of them can be used as a club should you need it and if all else fails, it is something for him to chew on rather than your body parts. I'd carry a bag of weiners to throw into the distance to distract him while I ran for the door and keep the cellie where you can get to it quickly.
The trouble with sprays are wind conditions. If it's a windy day or an unexpected gust of wind blows into your face just about the time you discharge the spray, you could get the full effects of the active agent plus the dog might still come once you're coughing uncontrollably and wheezing and the spray is slightly dispersed. I'd just be sure I was fully protected if I had to face a big, powerful, vicious, off-leash dog with any regularity.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |