not true, You CAN get rid of them. If you ever had broadmites, way worse than spidermites. I used{in VEG} forbid4f wiped them out. Sprayed the floor and walls only in flower room, Wiped them out. I would only use it in a severe infestation. Otherwise for spidermites. spray 3 times every 3 days with mighty wash, or get an airless paint sprayer for better results. mites will be gone. the reason you have a problem with them coming back is because pyrethins and neem oil, DO NOT work.
Forbid 4F (spiromesifin) is without question the strongest product available, and moves thru the leaves (not systemic though) so you only need to spray the tops of leaves. It kills eggs and miltes, which many products do not. It's incredibly expensive but you can buy a couple of applications for $25 on Ebay. I've used everything in the past and nothing totally worked- they always came back, sometimes worse then ever. Forbid is made by Bayer, and uses a process that punches holes in the skins of the mites and they die (dehydrate) in a day or two. It also lasts from 28-45 days so you may only need 1 application. Every product has good and bad points, this seems to be the "NEW" kid on the block and it works very well.
Mighty Wash, Neem, Azatrol, Azamax, Power Shots, pepper spray, alcohol wipes, Avid, Insecticidal Soap, Liquid LadyBug, Floramite.........nothing eliminated my probably all together except Forbid.
good luck
lol good luck only prob with spraying forbid is if you are close to flowering and you want to spray it, it could possibly effect your taste and/or smoke spraying it on the buds becuase quite frankly any spray to get rid of spider mites you need to soak every inch, nook, and cranny of that plant 3x over to make sure you get everything so there are many variables of mold, bud rot, smoke issues, taste issues etc etc please make sure you weigh your options of control of complete anihalation of mites, good luck 
