How do I teach my dog to stop ankle biting/nipping?

I am fostering, with a view to adopt, a lovely young man of 16 months. He is a Scottie/Westie cross. He is settling in fine ( it is end of day 4)...despite not seeming to have had much obedience training...I have started training him with the help of tiny treats/dry food....He is gorgeous, if rather arrogant...
I seem to have mastered "sit" , and "come" is starting to work...I've even managed to convince him not to eat the cats...but I just don't know where to start wth the ankle/foot/trouser leg biting...Do I ignore the behavior and give no attention for it? "No", is not working... I know that Scotties are known for being nippy, but I do believe this lad is very capable of learning manners!
Has anyone got any suggestions?

You could keep a house line on him inside so you can stop him doing it and put him in another room for a minute so he know it is the wrong thing to do. A water pistol also works with some dogs if the time out doesn't work.

Does he do it ALLLLLLLLLLL the time? It could be quite a tedious job getting him out of this habit.

I'd suggest clicker training. Treat him when he doesn't do it and when he does, ignore him until he stops, then immediately click and treat. When he gets the idea that to stop doing it = treat, prolong the time before you treat him. I.e, wait a few seconds after he stops, then treat, then when he's fine with that, wait a bit longer before treating and so on and just build up the time until he stops the behaviour completely.

Hello
What a great post, it made me smile!
Sorry he's a nippy dog though, but I suspect he won't be for long.
The best thing I've found to do is to stand still, turn your back, fold your arms and ignore him. The iNSTANT he sits (which he will eventually as he'll be confused by what you're doing) praise him calmly and give him a treat (handy hint...always have a treat in your pocket). You could also do some work aside form this on offlead heel work, jut getting him to walk nicely by your side with no lead, which will help when out and about too.
Good luck, great post, sorry about your problems but I did enjoy reading it!!!

Thank you all for the helpful advice...No, he doesn't do it all the time (thank goodness!)... but every time i walk up or down stairs...and, whenever the mood takes him, at any other time too! The ignoring thing seems to be starting to work...Bless him, he is fast asleep at my feet, looking like butter wouldn't melt...

ohhhhhhhhhh this is fun .. lol.. do you know how to do a fake fall- or "prat fall"? . What this is goes like this. Say dog starts biting your feet- near a wall is perfect. As the dog starts to bite your feet- slap the wall, and pretend to trip.. ( control your body).. Say : NO!.. AND do not make eye contact with the the dog for at least 10 seconds. Then go about your regular activities and wait for a normal approach. Or if in the middle of a room without a wall to make a sudden noise, pretent to trip and stomp your feet- make sure the dog is NOT under your feet- again- ignore the reaction for at least 10 seconds go do a activity like laundry or something or dishes.

Minnie would love it if i did that. She would think it was a great game getting mommy to trip

Thats why I said no eye contact, words etc a sharp No. No condolences.. Nothing.. Dogs hate to be ignored and this action they do get ignored and it was enough noise to make a statement ...

i have to say stamping my feet and making a loud noise, would make my pups attack my legs more...great game.
I totally agree with theb ignoring part though, I seriously think that is the main thing that is required and an instant reward should be given as soon as the pup sits nicely, which it will as it will be bewildered!

okee dokee...I seem to be winning with the ankle biting thing, thanks to lots of ignoring and praise when he's good...so, now I need help with knowing what to do about Mac making little wees (marking territory it seems) inside the house. Problem is, I keep not seeing him do it, so can't tell him not to do it!. Should I spray the entire house, top to bottom, with 'Dog Off'???!!!! Ha! and he's started chasing the cats again...Bless him!