Actually, I have a few general questions about the correct constructions that are used to describe the various "fasteners" (застёжки?) on clothing, not just tying the shoes or zipping the pants.

I'm familiar with the basic verbs involved:

застегнуть and расстегнуть
завязать and развязать
зашнуровать and расшнуровать

But here are the questions:

(1) With застегнуть, what is the usual accusative object that follows the verb -- the item of clothing, or the fastener on the clothing? In other words, would one say:

Я застегнул рубашку.

OR

Я застегнул пуговицы на рубашке.

(In English, you can say either "I buttoned the shirt" or "I buttoned the buttons on the shirt.")

If I'm not mistaken, when tying the shoes, one says either завязать шнурки or зашнуровать туфли/ботинки (but not зашнуровать шнурки) -- is that right?

And to express what type of fastener a garment has (i.e, whether it closes with buttons or a zipper or buckles or velcro or whatever) would you say, for example:

У меня две зимних куртки. Красная застёгивается на молнии, а чёрная -- на пуговицах.

(2) To say "her shoe is untied" or "your pants are unzipped", does it sound more colloquial to use the -ся form of the appropriate рас- verb in the past perfective? In other words:

У неё туфля расшнуровалась.
У вас штаны растегнулись. (or "молния растегулась"??)

OR can you use the short form of the past passive participle instead:

У неё туфля расшнурована.
У вас штаны растегнуты.

(3) Finally, what's the standard term for "Velcro"? Is it treated like an indeclinable noun such as велькро, or should one say "лента Velcro", or what? And does Velcro застёгивается, or is there some other verb like прилипается that's commonly used?

Спасибо заранее!

ЗЫ: I almost forgot! Is there a "polite euphemism" to tell someone that "The fly of your pants is unzipped"? I'm pretty sure every American schoolchild knows "XYZ, PDQ!" ("Examine your zipper, pretty darn quick!")