I had an Old English Sheepdog, took him to the groomers once, they had him for a full day and he came back ok so thought I'd have a go
First time I trimmed him, I shaved him a bit too short, where he was gray his skin was pigmented gray too, didn't notice I'd cut him too short until I moved onto his white areas which turned pink
He looked like Stimpy from the Ren and Stimpy cartoon
Couldn't finish him on one session as the clippers would get to hot to hold, sometimes I'd give him a mohican, lion mane or moon boots cut on the 1st session and then a week later would finish him off