Once you reach level 14, you’ll have the option to purchase the panties from Sandy. They’ll go right up onto your wall, right where Mary’s painting goes. If the cop comes and the panties are on the wall, he won’t steal any pots even if they do have plants in them. Tell him to piss off, and he’ll just steal the panties instead. Considering how easy it is to keep him off your back by just emptying out your pots, though, it’s kind of pointless to buy the panties.
The alien might be a nuisance, but when you are actively trying to level up, use him to your advantage. Build up as big of a stash of weed as you can while you are waiting for the alien to show up. Then when the alien shows up, trade him the huge stash of weed for his experience points. He trades experience for weed at a 1:3 ratio, so if you give him 3,000 weed, he will give you 1,000 experience points.
Another way to use him to your advantage is with the available in app purchase. Tap on the option that says “Warp to another level”. You’ll have the option to pay money in order to immediately gain an experience level off of him. Use this only if you have just gained a level or have no extra experience, but if you’re already pretty close to leveling up, then don’t bother. Of course, he will go away after you do this.
A glitched way to get all three of them to go away is to wait for Lucy the stripper to show up after one of these three guys shows up. Do a lapdance with her, and tip her all the way through until she strips completely. Back out, but stay in her menu. Then get back into the lapdance and tip her again and the game will crash. Reopen the game, and often, the cop, gangsters or alien will have simply disappeared with no trace in sight.
If you have a ton of cash and you want to upgrade all of your pots (say, after you unlock the alien pots), just plant weed in your lower tier pots and wait for the cop to show up. Tell him to piss off and let him take away your old pots. Then buy your new alien pots and start using them without ever having to worry about water again.