My westie's runny poo

I have a 3 year old westie who will be 4 next month. Basically when he goes to the toilet in the garden he is fine and his poo is solid, but once we take him out for a walk this changes his first poo is still relatively solid but his second is runny and anymore after that will be runny so im wondering if anyone else has had a similar problem or knows anything that can help resolve this problem.

Thanks in advance

Lots of dogs get the same problem it's caused by the exercise.

Hi GC84 and welcome to Dogsey.
As Trouble says this is not unusual with many dogs and seems to be exercise relate.

When dogs go for walks they find lots of stimulating scents, anal gland secretions which are used to mark territory may have an effect too.

My two are the same. I agree, it's exercise related. Pity it wasn't more solid all of the time, would make life a little easier clearing it up!