$\displaystyle \int \tan^4\theta d\theta$

I know you're supposed to use the identity $\displaystyle \tan^2\theta+1=\sec^2\theta$

so, $\displaystyle \int \tan^4\theta d\theta=\int (\sec^2\theta-1)^2 d\theta$

now I don't know what to do next. Can anyone give me some pointers to get moving?

Thanks