"Who Shot the Hole in my Sombrero"

I've been after it myself, and found out this much.

It was written in 1949 by Milton Leeds and Billy Hayes, and has been recorded by quite a few, most notably Rex Allen, one of the old singing cowboys, and narrator of countless Disney documentaries.

Disney has an an animatronic exhibit called "America Sings" where the singer is an animated dog seated on a burro. He sings a shortened version of the song, but no longer with the heavy Mexican accent he had originally. The PC folks sanitized his accent some time ago.

I have located a copy of the sheet music and will let you know when I get it, if no one finds the lyrics first.