I used to use pink and blue correction fluid but it's become hard to find (particularly blue). Other than ribbons or collars around a puppy's neck, what do you use to tell your puppies apart?

Do you use paint, nail polish, or some other method? If you use something like paint, what brand and how long does it last?

I don't want to use anything around the puppy's neck for a couple of reasons - mainly because it can come off but also I get nervous about accidental choking. I'd like something that lasts at least a few days even with the mother cleaning the pups. I'm also not big on clipping hair because it seems hard to see without actually picking up the puppy. I like to be able to tell them apart from a distance...

-N

I have used nail polish for over thirty years with great success. I use the cheap, quick dry kind. They don't like the smell, but if I hold them on my lap work the liquid into the fur and let it dry for a couple of minutes before placing the pup back in the box, it works great. You have to be sure to put enough "into" the fur, not just on top, to keep it readable. I reapply about twice a week.
I have used different colors and mark on different parts of the pups's anatomy. Head, back,tail, shoulder, etc.

I use embroidery floss (cotton)...it is only six strains of thread twisted together. Make sure to get only the cotton type......it is much finer than the cheap polyester type for crafts. I have used it for over 15 years and never had a problem. I put them on leaving only a finger or two of space around the neck.....the collars actually blend into their coats. If you put them on too loose they will slide off. I check the tightness everyday couple of days and change them when needed.

I method I use alot also is to clip a chunk of hair in different parts of the body (example blunt cut tip of tail, left shoulder, right shoulder, left hip, right hip...etc) Re clip once a week since hair does grow out quickly.
When I use rick rack collars I will also clip since sometimes the little darlings love to get their collars off, but with the clipped spot they are still marked.

I use Acrylic Artists paint in different colors. It's non-toxic. Refresh about once a week. It will come off with warm water. I've tried the yarn and string and have had them come off.