Saddle slipping back

[connemaragirl]

Hi guys!
looking for some advice on a saddle slipping back
i have just got a new horse and when I have been riding the saddle just slips back
Sunny doesn’t wear a martingale or breastplate. 
Sunny came to me really fit, he has a low wither and I have only had him a week so was wondering if that may have an effect. 
He wears a simple girth and was wearing a stud girth at his last home. 
I think the saddle fits...
was thinking a breastplate may help. 
I will speak to owner tomorrow, sorry for a bit of a ramble
thanks for any advice
Millie

[clipclop]

Get a saddler to come out and check the fit :-)