For many demons, there are a lot of deterrents. For the more powerful ones, and if your concern is with the ars Goetia then you are talking about powerful ones, there is very little to be done to keep them away. Honestly, I was not aware the ars Goetia were making attempts on mortal worlds recently, so I commend them for their subtlety and you for your apparent ability to counteract them. One thing I can suggest is by finding their angelic counterpart. The ars Goetia are an immortal family, like myself and my brothers, as such, Heaven has a proverbial counterpart to us. If the angelic counterparts maintain a close watch on a reality, it will hinder the demonic counterparts' ability to gain a foothold in it. That being said, they can't be in every reality at once, so keep in mind that by saving your reality you may doom another one that is not as well prepared.