I've used These bird bath heaters with our mirafount cattle waters and never had any issues with shorting over 10 years using them
Just make sure to keep the cords out of reach cause our cattle like to chew on them
I only have a few hens and it’s within a reasonable extension cord length. So I have this: Farm Innovators Model C-50... https://www.amazon.com/dp/B0002DHBDY?ref=ppx_pop_mob_ap_share It has worked well so far for me.