One of the reasons for those "call before you dig" signs is to keep people from inadvertently cutting through power lines, but the main reason is to keep people from accidentally opening portals to hell, as depicted in the haunting cautionary tale The Gate, starring the haunting cautionary tale Stephen Dorff.
Dorff was only 14 years old when he took the lead role in the movie that would launch his film career and make him a household name. (Eventually, I mean. He's still working on it.) His character, Glen, is an ordinary suburban kid with dog, a big sister, and a portal to (SPOILER ALERT) hell (END SPOILER) in the backyard, except that we don't know about the portal at first because it is blocked by a tree that evidently sprouted up out of it. This appears to be a perfectly good tree, with a tree house and everything, and there is no logical reason to cut it down, so Glen's dad cuts it down. This prepares us for the movie's overall sense of logic, i.e., it does not have one.
Glen and his nerdy little friend Terry (Louis Tripp) are playing around in the leftover roots and stuff when a plume of toxic-looking smoke leaks out of the hole. This is our first indication that removing the tree has led to a hell portal being opened, apart from the fact that the movie's poster and DVD case explicitly state as much. Glen and Terry disregard the plume of toxic-looking smoke because, hey, if you're going to obsess over every single supernatural thing that happens to you, you're not going to have time for anything else.
Glen's parents go out of town for a few days, leaving him in the care of his not-quite-16-year-old sister, Alexandra (Christa Denton), who immediately throws a party for all her dumb teenage friends. The party is PG-13, though: nobody's drinking or fooling around; they're just dancing and, when things quiet down, telling ghost stories. They play a spooky game where you can supposedly make someone levitate by touching them and concentrating, with Glen as their subject ... and he actually levitates several feet in the air before falling to the floor and freaking out. The teens think this is hilarious. Nobody other than Glen is at all curious about the fact that he just did something that isn't possible.
Now we know for sure that something is amiss. Not with the house, with the movie. Any movie that has demons disrupt the laws of physics in a room full of people, only to have all those people not notice or care, is a movie that has some serious problems. What's your deal, movie? You need to tell us WHY they ignored the levitation. Here, I'll help you come up with some explanations. Maybe the demons messed with their minds so they didn't see it. Maybe it only happened in Glen's imagination. Maybe all the teens are tripping on acid. I'm just spitballing here, movie. Meet me halfway.
At any rate, still freaked out about the levitation thing, Glen has Terry sleep over. (Terry wasn't in the room when Glen levitated. You're in the clear there, movie.) In the middle of the night, Terry is beckoned downstairs by the ghost of his dead mother, but when he embraces her, she turns out to be Glen's dead dog, which is why experts advise that you should never hug a ghost without seeing some ID first. Glen's dead dog was alive earlier that night, by the way, but it was very old, so its death is not a surprise. Terry hugging its corpse would be surprising, if the bar for "things that surprise these characters" had not been set so high.
Glen and Alexandra don't know what to do with the dead dog, so they give it to the boy Alexandra has a crush on and ask him to drop it off at the animal control office. But the office is closed, so the boy dumps it in the hell portal in the backyard, because why not? Meanwhile, Glen and Terry use their knowledge of heavy metal music and a book of demonology Terry has lying around to figure out that the weird events of the past 24 hours are associated with the hole in the backyard -- you know, the hole that expelled a plume of toxic-looking smoke at them. They further deduce that the dog's death is a "sacrifice" that has activated the hell portal, even though the dog died of natural causes. This either means that someone killed the dog, or that Terry and Glen don't know what a "sacrifice" is. Either is possible. The movie, you will not be surprised to learn, does not follow up on this subject.
Then we start seeing some actual demons. They're little troll-like things, about the size of monkeys, made out of clay and stop-motion animation. They scamper around the house trying to kill the kids, who are now legitimately surprised and terrified (FINALLY). More random weird things happen, like Glen being touched by a demon and coming away with a functioning eye on the palm of his hand, which he stabs out with a pair of scissors, even though it would be pretty useful to have an eye there. Like if you wanted to see if something was on a top shelf, you could just reach your hand up there and look. Anyway, the kids try shouting random Bible verses at the demons, but this has no effect. Then a really big demon emerges from the pit, and Glen kills it by launching a toy rocket into its chest. Then everything is back to normal, and the dog is alive again, and none of the neighbors heard any of the terrible commotion going on at all hours of the night.
The Gate is aimed at kids who are about the same age as the characters. This is presumably why the filmmakers focused on the special effects, which are pretty good, rather than the story, which is terrible. Sometimes you slack off when the only people you're trying to impress are 12 years old. Then again, maybe it's not fair of me to make assumptions. For all I know, these guys would have been just as lazy if they were making a movie for adults.