I put an extreme weather disclaimer on my profile. Feel free to copy and make changes to suit your own policy. The temperatures I listed are veterinary guidelines. I have one client I need to be firm with but everyone else has been wonderful.
"About Severe Weather: I take all weather advisories seriously!
* When the heat index is above 90 degrees, walks will be cut short for your pet's safety and for my own. We will use up the remaining time getting pets and belly rubs or playing in doors. Water will be available for your pet on our walks.
* I don't mind walking in the rain but thunder and lightning is where I draw the line. Walks may be early or delayed depending on the forecast. Your flexibility is appreciated.
* In winter, if the temperatures dip below 20 degrees we may need to talk about turning our walk in to a drop-in visit.
I will always communicate with my dog owners if a change of plan is necessary due to dangerous weather and temperatures."