What condoms are you using? What size is your dick? Maybe the condom is a bit loose? As in too big?
I've never had a condom roll back up except when I go soft obviously it does then. Are you sure you stay fully hard?
Most times condoms are too tight. Especially normal ones. Try some with a tapered fit.
I also think that it is a "condom size" issue.
In my experience, small condoms (if not so small to make me loose the erection, like regular condoms) just roll up half way the shaft.
Anyway a precisation could be helpful: does the condom roll up alone, or when you start penetrating?
In the first case it sounds like it is too tight, in the second too loose.
Your penis gets thicker the futher down the shaft. that makes the condom roll back up.