I wonder if you are asking about Leylandii? or deciduous trees? Assuming they are yours and not protected trees?
Cut them down and use a stump grinder to remove the roots or apply stump killer to the stumps as soon as they are cut down this is a cheaper option but will take some years to rot down.

If you are talking about leylandi ( and many other conifers) just cut them off at the ground and they won't regrow.

Dig them out.

I read that hammering copper nails into the trunk does the trick. But you would still have to cut it down.

I guess covering the cut down tree with a heavy duty opaque sheet would stop it regrowing. Things cannot regrow without light