Hi Larnie!
I feel your "pain". I've been out for over 20 years and am contemplating getting back into the gig.....and since I've made that decision I've noticed exactly what you are talking about (and thats observation, not work, I'm so not ready to work on other people yet).
Back to the matter at hand......my middle daughter is a biter and a bad one at that. Some days it looks like there is inground dirt around the entire nail cuticle to end. Drives me insane, but its working. I've got her on a program now to help her grow out but this is what I do with her.
I remove whatever polish she has and I soak her hands in the hottest water she can stand to soften the skin (cos as you know biters have leather cuticles, etc). Then I massage solar balm vigourously into her cuticles etc. (calms her down too actually). Once that is done we wash with a nail brush and a cleaner that I have from the hospital (disinfectant) so its all good. Slowly I work with a blunted orange stick to get it all out, trim hangnails where necessary and have her wash again.
Now I don't do enhancements on her as she is only 8 and your question is relative to enhancements, but if I did, I would make a custom mix for her (geeg's is on here somewhere, if you do a search) for a mask pink and natural.
Send them home with an aftercare kit that includes a nail brush and the cleaner you decide to use with whatever system (not sure what NSI offers, but the geeks here can lead you in the right direction). and solar oil.
I say the last because I am a biter too and had those same issues and found with religious use of the Solar Oil, a lot of the dirt loosened itself after I had the enhancements and as long as I made a routine of brushing and oiling by the time the free edge was out, it was clean as a whistle.
sorry so long, but I hope this helps....and good luck!