I always do insulin IM and usually in my inner forearms. Once I go past around 75IU some will leak when I pull it out so when the doses get up there I split it into two shots.
Lantus itself doesn't make you insulin resistant. I used it 5-6 days a week last year and it took months for resistance to develop - though I used it on a rebound so I was super primed. You avoid becoming insulin resistant through eating a mostly clean diet, consuming less carbs on rest days, using metformin instead of insulin on rest days, modulating GH use, using GW-501516, getting plenty of sleep - there are many ways.