A walking stick and training might be a good idea and will serve well into later years. Pepper can sometimes fail and can also blow back in your face if the wind is strong and coming from a bad direction, so caution is needed when implementing this method. A pocket knife could be a last ditch final line of defense but you would need a rather large knife and I'm not sure how laws in your area will affect that.
What sort of activities is your friend participating in when the risk of a dog attack presents itself?
Disequilibrium facilitates accommodation.
9mm vs .45 ACP? The answer is .429