You have eight stables? Are they full/part or DIY? How many are full? We only have full/part and are full at the moment with a waiting list, but it takes a long time to get to this point, not just a few days. When I have a space on the yard I advertise it on my website and use google adwords to attract traffic to the site. When we are full, I switch off adwrds and state we are full on the website. We still get the odd query though and those are added to the waiting list should they want to be. We also get countless enquiries for DIY despite stating that we do not do DIY on our website. So I would say you get around ten times the amount of people wanting DIY as other types of livery. But I would never do DIY.
An advert in Chiltern & Thames Rider might help, and put adverts up in all the local feed and tack shops. Also list it on as many websites as poss H&H, ******* etc.
I think people in this area expect good facilities, and services. Our yard is full, and I can think of several other nice yards in this area that are also full. As well as all the local people who have horses, many people who live or work in London also keep their horses out here, so there's potentially plenty of customers if they can find you, and if you can offer what they require.
try advertising through pony club and riding club as well. A website is a must now days and I found when looking for livery I was more reluctant to call a yard if there was no website as ridiculous as it sounds.
I would also invite round and stuff with fizz and nibbles the YOs of the good similar livery yards who are always full, and then they can once theyve seen your set up, pass on people who contact them about livery but who they cant take cos they are full. Its no loss to them as if they dont have space they cant take them on. You might get some ideas on marketing too and also on services they offer or their approach that makes them so popular.