What's the best way to kill a giant conifer tree?
The best way is to take out the tree in sections, cutting it down then having the stump & it's roots contained. The easiest way is to contact a tree removal service company to take care of it. Although, you can always use a stump grinder, & dig/chop out the remaining portion, once the majority of the tree is taken away. However, given it is large. You may wish to simply go with a Tree removal service, because the hassle, time and danger of doing it your self, may not be worth it. That though is ultimately you're judgment call.
What did you have in mind any way?
if you grind the stump down you shouldn't have trouble with it coming back, and the roots usually take care of themselves, eventually rotting away underneath the soil if you don't remove them.. the ground will sink in lines where the roots were when they rot away.
im going to paving slab my garden but i have 7 conifer trees im going to cut down but how will i get rid of the roots if i cut the stump rite down and put root killer onto it will it grow back or will i have to dig all the roots out completely