Well the first thing that comes to mind is how do you know they are intruders? Sometimes "intruders" are really just spirit guides trying to contact you. Sometimes they're just spirits trying to get attention. But more often then not intruders represent unsettled aspects within ourself.
Regardless you can prevent unwanted visitors through the use of magick barriers as in you use magick symbols to cerimonially seal your room or grant yourself protections. You can create an amulet or wear a delta pendant. I couldn't find any good pictures so what a delta pendant is is a necklace with a silver or stainless steal equal lateral triangle with cross bars that intersect in the middle. It represents a gateway that prevents unwanted visitors from entering your dreams uninvited. The more practical solution is to buy a dream catcher as those also prevent unwanted guests from entering your mind. Also the use of dream wards can repell invaders. Dream wards can be grotesque masks, or statues made from clay, beeswax or really anything that can be shaped into the figure of something like a gargoyle. And the last solution I can think of, which is what I use the most, are dream servitors. I don't really want to get into how to make servitors, just use the search function and you'll find information about them. Study up and if you like what you read make one with the intentions of protecting you from intruders.
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