What's the Name of That Book??? discussion

I remember this book being a series and this wasn't the first book in the series. It was about a boy/child/teen who was with a fox who was being chased or was at least very smart. He would talk about these dog figures in long coats which would give me the impression they were like spies or agents looking for this fox. I remember them walking in a different world than earth but the boy/child was from earth and the fox was explaining a lot of this world to him.
I read this between 2000-2012 or something. The book was new at that time. I think it was a YA.
I can remember that those dogs were named marauders or something.
And the cover was dark blue with several dogs in the long coats looking at me and walking along side the cover.

Janine, how did the boy travel to this other world?

I copied some book details to the topic header. Feel free to edit it.

The fox and the doglike pursuers remind me of the hounds of the morrigan by pat O’Shea, but that’s not part of a series!

@Emily OMG YES THATS IT!!
I have no idea why I thought it was a series.
Thank you thank you thank you!!!

Great! Glad you found your book, Janine. Thanks for the update.

The Hounds of the Mórrígan by Pat O'Shea - Emily's find