good insulation and proper ventilation.
thermal imagine cant see through walls. so if you have an inclosed grow space that is fully insulated, you wont need to worry much. plus in the US, in almost all states, a warrant is needed to use thermal imaging, so they will mostly be using it to back up what they already suspect. so if you keep everything else on lock you wont need to worry much.
there still are some states that use random scouting planes with thermal imaging tho so make sure you are checking the temp around your grow setup often.