If Sasha pulls a bt on lead then perhaps thats whats doing it or perhaps you've got the collar on too tight??...

I'll plug the GAL shop now, Esther sell's really nice 'slip' collors, the hang loose round the neck when walking but if the dog pulls they tighten up a wee bit so are completely secure (they are like very comfy and not at all cruel choke leads)..Esther also sells nice indoor collars, don't know if you keep Sasha's collar on in the house, if you do then you could perhaps try one of these indoor, works on the same principal as the 'slip' collars but are made of fabric, dead comfy!