First off - welcome to TCS!
When a cat urinates inappropriately, I always recommend a urinalysis be done to test the kitty for a UTI (urinary tract infection). While they may appear physically healthy, it's possible they have a UTI, which will cause them to urinate in the wrong places - and can be life threatening (neutered male cats are especially at a high risk to block up & die).
Just because a cat is neutered (or spayed) doesn't make them fat. Most people who fix their cats keep them indoors, where they often lead a more sedentary lifestyle - and being sedentary leads to them being fat. Not many people have altered outdoor cats.
I do encourage you to make a vet appt (yes, pay the vet more money) to discuss the weight gain and how to safely take the weight off - and also discuss the inappropriate urination.