Is it yours for keeps or does he want it back?

这东西是永远属于你了，还是要还给他？

His genes are for keeps.

他的基因是用于传承的。

This gold medal is yours for keeps.

这个金牌永远属于你。

I'm in him for keeps.

我是吃定他了。

This time I am giving it to you for keeps.

这次我把它永远送给你了。