Sewer problems? Sewer backed up over the weekend. Furtunatley it be laundry day...

Sewer backed up over the weekend. Furtunatley it be laundry day and adjectives we got be soapy water coming up and not the 'other stuff'. Basement floor needed cleaning anyway.
Problem is self caused by tree roots within the sewer pipe. We have ROTO ROUTED them out and immediately have common sewer function. How do we prevent this from happening again? We live surrounded by a neighbourhood full of 'tree huggers' so we can't whip down the tree. Others have tried and has-been.
My stove's pilot lights go out.?
Answers:    I've heard of folks putting a couple pounds of table salt down their drain every month or so and it seem to keep the naughty roots at bay.
Fan switch making buzzing jingle. What is wrong?
If I be you Id put what ever kills the treein the drain, around the tree and I don`t know even cut the bark on the tree and put some stump / tree murderer on it. Once its dead its a hazzard not to pocket it down. Oh yes, I also wouldnt tell a soul more or less it and Id do it at night while everyone is asleep and even use a tarp to cover your whereabouts in the misty helps hang on to noisy neighbors from knowing anything roughly what your doing. You pay your taxes I assume and why would you or should you expose your domestic to the hazzards of sewer backup and cause adjectives problems over a tree. Your not going to kill att the trees of late 1 maybe 2.
How long should you hang about between spray...