how do i keep my indoor kitten from trying to run outdoors?

[lbear]

i'm guessing he must of been an outside cat cause whenever we try to leave he will wait by the door to get out. can't let him outside cause we live right across from a major highway. can't let him in the backward cause we have some gaps on the bottom of our fence and he would be able to fit through them. can't let him in the garage cause there are some gaps in the bottom of our garage door and i'm afraid he will get out. he likes water so spraying him with a water bottle will not do anything. he actually got outside yesterday i took me half an hour to get him back inside. he also does get in our garage a lot. does anyone have any advice on how to get him to stay indoors? also he is only 12 weeks little younger/older give or take. the person we got him from lied about how old he actually was found out he was only 6 weeks after we got him (vet told us how old he was) so he is not old enough to go into heat so i know that is not the problem we want to wait for a couple more months till we get him fixed.

[Fender]

i think the only way is forcing to be inside, make the indoor a place he can enjoy, toys and play platfors where he can climb and jump around. don't feel bad thinking he will be sad inside, i read somewhere an indoor cats lives more time then out door one, cause they are not exposed to predators, and as you say you live close to a highway...