I built a cookie tin fount warmer five yrs ago, and it will be put back into use again this winter. For the most part, I use a 40W bulb. But, I have found when the temp gets to 0 F, It needs a 60W bulb to do the job. The tin never gets hot enough to even think about starting a fire. You can at any time, place your hand flat on it. Unless you dunk this thing under water, you have nothing to worry about. The bulb is safely enclosed in a tin can, water splashed on it won't do anything, unless you had no idea what you were doing when you built it, and have the electricity shorted to the tin. I used a old piece of romex (12AWG), for the electric supply cord. Chickens don't have teeth, they are no threat to that cord, or even a regular extension cord. Mice could be a threat, and if you have them, just run the wire through conduit. We are not talking rocket science here.
I say this, I trust my $5 cookie tin heater waaaaay more, than I would trust that near $60 RedChinese engineered piece of junk they sell in T/S. You don't know when that thing will crap out, and it will, and you are out $60. The bulb burns out in the cookie tin, in goes another cheap 40W bulb, and it's back in business.