Subsitute Dog is a web-doujinshi by copycat404 for Courage the Cowardly Dog. It is about well... a subsitute dog named Condor. Condor replaces Courage while the latter goes on a vacation.
Substitute dog part 1 by ~copycat404 on deviantART
Here's the deviantART folder if you want to read some more.
It's pretty funny, you know! And do you know that it includes a character from another show? Wanna know who? Well, you gotta read it, oh yes!