Hi
Excellent advice from Goose4462 and covered most of what I was going to suggest.
I would use as many sale/advertising options as possible on start up, as every sale counts. DON'T overspend on advertising! So much can be done for free or minimal costs (E9 per month on here...Justin didn't mention it in case he was accused of spamming LOL).
Build yourself a website and blog (with good SEO) and make sure when you post anywhere on the WWW you include your link. I would go with wordpress for the blog because it seems to generate more web traffic than some others and you can have an online shop on it, as well as the website. I would have one main .com domain and then some sub domains ie .es .co.uk .net and .biz. etc. Do lots of searching for the best purchase price and hosting. Make sure the web address you choose is related to your biz..
Make use of all the free papers...don't just limit yourself to Spanish ones, as people who have homes in Spain live all over the world and crime happens everywhere. Vista Print are good for leaflets and business cards...don't be shy handing them out! Set up a facebook page. A twitter account. Set up a Lindkin page. Join networking groups.
I think with a small, low priced item your main aim should be to supply wholesale. With trusted main stores SOR costs them nothing, but could make you lots. I would even approach stores in the UK (B&Q/Wickes/Homebase) because glass/nails/barb wire is illegal on fences/walls here...but your product isn't.
There's lot's of ways to promote and market your goods...write them all down and you'd be amazed what you can come up with.
Once upon a time trade was limited to our hometowns and a bit beyond...you can now go global with ease.
Believe in you and your product.
GOOD LUCK...hope you do really well.