As far as protection goes it depends on a few things including how much work you're prepared to do. Like most astral protection it comes down to creativity and visualisation whether you're in the astral planes or not. A simple banishment could work (look up the Lesser Banishing Ritual of the Pentagram which includes a protective barrier once you've banished any entities actually in your presence. It may not suit you and you'd have to practice to get it fully effective). You could set up astral "gargoyles" in the 4 quarters plus the intermediate points. NE, NW, SW, SE. You have to decide their shape and form and establish them through meditation in the temple of your mind.
The rest brings up a discussion of how much of these "telepathic" engagements are your imagination running riot or real entities trying to get to you - and, is there any difference between the two (in that an imagination running riot could be the work of astral entities)? The best is to contemplate on what's going on. If they seem very real then try to talk to them (always polite) trying to find out what they want from you. Why particularly you?
Or try yourself to rationalise what these encounters are about. What do you think they want from you? (Treat it like a silent interview in contemplation.) Can you disperse them when they arrive? You evidently know when they're about - can you let them into your presence then banish or dissolve them - there are techniques for this. Could they be trying to guide you (here, you have to be careful to avoid delusion - there are plenty of tricksters out there and if you're vulnerable they might lead you into trouble).
Have a go with these things. This is a more active approach than prayer, like "calling on God for help" although that might work too. Reading psalm 69 aloud is good for general protection when you feel in trouble. I don;t know whether crystals or stones would work - one advantage (if they did) is that YOU don't have to do any work!
But mainly, believe in whatever you do.