New Neighbour

We have new neighbours & for the first time a dog next door. Which is fine,except there's a gap in the fence just big enough for a nose to fit through!
Now the collies don't mind at all,but if this dog leaves his nose poking through for too long I fear that my terrier Boo may just have a bite of it!
I think filling this gap will have to go on the list of 'to do's.....near the top!