I've been singing it for over 15 years (and referring to it as a "south of the border ballad") with a few variations on the above lyrics. Knew Shel Silverstein wrote it, but never ran into a recording. Since my random access memory is getting more and more random, I'm not certain who, exactly, I stole it from, but a likely candidate is Judy Cook. I finish it with a chorus of "la las" (ending with a flat one) but I may have stolen that idea from her, too.

I just love the line "I never thought you were a squealer, Sheiler"...

Linn

(chorus)
       Pour me another tequila, Sheila
        Take off your red satin dress.
        I crossed the border and I beat the dealer
        For all the damned gold in Juarez.
        I feel like old Pancho Villa, Sheila
        A fast horse and gun is my friend.
        So pour me another tequila, Sheila
        Lay down and love me again.

No I can't tell you about it.
So just leave the gun by the bed.
I feel kind of naked without it,
But it eases all the fears in my head.
Pass me the salt and the lemon
And bend down and blow out the light.
I never much trusted a woman before,
But, Sheila, I trust you tonight.      [ I added, spoken, "Big mistake"]
(chorus)

Sheila, I'm feeling your heart beat,
But I can hear footsteps outside.
The courtyard is full of them damned Federales.
Sheila, there's no place to hide.
I don't know who could have led them here
'Cause nobody knew it but you.       [point to someone in audience]
I never thought you were a squealer, Sheiler
Now there's just one thing to do.

        So, pour me another tequila, Sheila.
        I'll put on your red satin dress.
        And you'll put on my clothes
        And go out and face the dealer.
        Sheila, I wish you the best.    [wave]
        I feel like old Pancho Villa, Sheila,
        A fast horse and gun is my friend.
        Pour me another tequila, Sheila,
        (Pour me another tequila, Sheila,
        Pour me another tequila, Sheila,)
        I'll cross the border again.
        La la la lala, etc.