What you can do
If you are stopped by the police, make sure to not panic and just relax
Just remain silent
You have the right to refuse to allow the police to search you.
This may not prevent the search, but it is the best approach to preserve your rights in the event that you end up in court.
What to do
First things first, if there are any people present that could potentially serve as witnesses, make sure to obtain their information.
Always make sure to make note of anything pertaining to the officer(s). This could be their name, their badge information, etc.
Make sure you file an official complaint after the incident.
What to do
As the owner or resident of the house, you have the right to not let them in your house, unless they show you a warrant with information pertaining to you. Until a warrant is presented, you are allowed to not let them in.
You do not even need to open the door. You can ask the officer to show the warrant through a window or put it under the door.