 
 I had this exact problem in an apartment. What worked was a short reset talk on a neutral day at the door, not when they were asking. I said, "I've realized I need to be more protective of my stuff and time, so I'm not lending household items anymore." If they pushed I repeated, "I'm not able to lend that," and redirected with, "The corner store one block over will have sugar or tape." For parking I used, "That space is assigned to me, so I need it open at all times, and if you are in it please move now."
Then I backed it up with simple routines. I printed a sign that said "Reserved Unit 3B 24/7" and taped it by the spot, and I saved two quick texts in my phone notes: "Hey, it's 3B.
Need my spot free now, thanks" and "I'm not lending items, but try the corner store two blocks over." Each time they tested the boundary I used the same sentence and did not explain further, and if it happened again I left one dated note under the wiper, then emailed the property manager with photos. If spots are not formally assigned where you live, check the building policy first and point to that in your wording, and the whole thing took me about an hour to set up and a few minutes per incident until it stopped within two weeks.
 
  
 