i just wanted to say, thank you for seeing both sides of the argument, as someone who has worked extreemly hard on her garden i can honestly say i personally wouldnt apreciate it if someoens dog came up and peed on my garden/bushes. our dogs have an area of the garden they are allowed to pee, poop, dig run and tear apart, the flowerbeds and front lawn however are off limits and they are very good about staying off, YES fertilizer has amounts of amonia in it, but just like when you over fertilize, if every dog that walks past that bush pees on it, eventually the bush is going to get severe amonia burns (and yes it will build up fairly quickly) and it can perminantly KILL the bush.
i think this neighbor could have adressed the situation properly by asking you nicely, please dont let your dog mark my bushes, every dog is doing it and its slowly killing them!
and hopefully you as a neighbor will realize, while one dogs pee is nothing, when every dog in the neighbourhood is marking that same spot it can easily do permientn damage to someones lawn/garden!
most places have a grassy patch between the actual road and walkway, if so i see nothing wrong with using this as a spot to relive so long as poop is cleaned up. when your dog is peeing 20times in 45 minutes that is teritorial marking and a behavioural issue that can be controled, you are supposed to be the alpha dog, and if hes making you stop every couple minutes to mark a bush or fencepost then hes the one in charge of the walk...if he NEEDS to pee fine, but no healthy dog needs to pee 20 times in 45 minutes, let him do one good pee if he needs it, then when you see him sniffing at anything on the walk that would involve lifting the leg walk on by, when you find an open grassy area neer the end of the walk again give him the oportunity for a pee if he didnt do one at the beginning.
i woudl also find as many of the dog owners in your area and see if theres any interest in getting a dog park put into your local area so you HAVE somewhere safe and apropriate for your dogs to run play and go potty. many of your none dog neighbors will also sighn a petition in favor of a dog park when its explained to them that if you have a dog park more people will take their dogs there and less dogs will be using the sidewalk and gardens as bathroom areas.
next time you see this neightbor just let her know you understand why shes upset, and will try not to let it happen again, but next time if she has an issue youd apreciate it if she could aproach you respectfully and she will be treated in kind