I have at last cracked this problem after various proto-types and it is very simple as follows:

Cut thick plastic food bag in half from top to bottom, cut off some of the top.

Place dogs foot in the corner of the bag with the long side at the back
Fold bag in and secure with parcel tapejust above foot
Cover the whole of the foot area with duck tape making sure it overlaps well.
Cut off bag so it finishes just below top of dressing/plaster
Use parcel tape to secure bag to leg and top of dressing

To remove cut though parcel tape at top and slide "boot" off so it can be reused the following day, it if starts to look worn then add more duck tape.

Christine

I have found bubble wrap works really well too and it's usually thicker and takes longer to wear through as well as providing some cushioning.  Good, if it's a cut pad.

I'll try that if this one wears though - the duck tape reallys seems to stop the grit etc making holes it in so it leaks

Christine