Neighbor taking out our shrubs, need an affordable safety fence!?

In the last year our unfriendly (but hadn't been hostile) neighbor has seemed to be going through something which seems to be getting worse and worse. He has never talked to me in 5 years, but one sudden manic moment told me all about how the cops had taken his friend away and now had a restraining order, and how he'd been sick for a year and lost a ton of weight. I never knew anything about him, though tried to say hi and had for years left holiday cards, but all in 1 conversation learned more than I would normally have learned in months. He never talked to me again since (that was 6 months ago) and since then he has had new friends move in/out, had men stopping in front of our house at 3:30am beeping (I could see the man's GPS, so I figure he didn't know the neighbor much since he didn't know where he lived), and recently had his new live-in friend taken out by stretcher unconscious at about 4pm (I'm only guessing drugs, but don't know, but he had told me in that one conversation that his last friend had been drunk and doing drugs the night he was arrested). All of this story is to lead up to why I am more worried that he is getting worse, more unbalanced. His house is very close to our's, and a few days ago he walked onto our lawn while I was home with my baby and pulled out a bunch of our shrubs along our house that my husband had been growing for years. Our neighbor is a cop, and he told us his wife saw him do it, and it makes me think this neighbor is getting more and more unbalanced, and I'm scared, and a new mom, and so nervous to be in our little backyard with my baby. We have a little fence between our yards halfway, but it's only about 3 ft high. We don't have much money but I'm desperate to put in a higher fence! I've been researching putting in our own fence, but we can't afford the put together fences I found online (I called the town hall, and we can have 6ft tall, and can be on the property line, but the man suggested leaving a foot). I have been trying to think of ways to build a fence, or find used lumber, or maybe buying some inexpensive mesh? I saw rolls of mesh on one site and posts, and also saw faux ivy screens that might make more privacy, but my biggest concern is safety, and keeping him/anything out from his side of the yard. It may sound like I'm being a nervous mom, but I have heard the screaming from outdoors at 3:30 am, and heard banging on our backdoor one night, and think he or is ex-boyfriend may have hurdled our little fence, so I really have been scared to go out. On a tight budget, is there any way that someone can build some kind of fence? We do have a fence in the backyard (the 3 ft one) so there are some posts there, but not on the area abutting his driveway, where he tore out our shrubs, and where we're always finding trash and cigarette butts. If anyone has any suggestions, I would be so grateful! Thank you!