I have seen stray dogs outside the gates before and they do tend to move on eventually when left alone. The problem being that just like in the UK there are many strays and a shortage of places at rescue shelters for them and many do get destroyed. There are less animal charities and donations in Spain than the UK and although I understand your concern personally I would hate to be the person who reported the dog and ultimately was responsible for the poor thing being killed. Many of the pet dogs at CDA are strays and neglected dogs that have been adopted by residents and have made wonderful pets.
Where-ever you go in Spain you will see many strays but they seem to look a lot happier than the strays in the UK, must be the climate that suits them. Most of them don't cause a problem and tend to be quite shy when approached, but as the resort is busy at the moment the stray dogs will be getting fed more than usual. You could always contact Noah's Arc, I don't have a number for them but they have charity shops at Camposol and in the port and they may suggest something. We use their shops to donate decent items to instead of dumping them in the CDA skips, this at least helps to boost their funds and we always land up buying second hand books, DVD's or jigsaws from them.
Bee.