Father Wants Me To Repay College Expenses (calif.)

My father is claiming that my college expenses were a loan and he wants me to pay him back. I'm surprised because he never said it was a loan at the time, and I don't remember signing anything (I think if I did, he would have produced it). Over the years he has asked me to repay the "loans", but I have never acknowledged them, verbally or in writing.

My father isn't doing well financially after my mother passed away, and has asked me again to repay the "loans". I'd like to help him out, but I'm afraid that any money I give him will be seen by a court as acknowledging the "loans" and obligating me to pay them.

Is there a way to give him money without risking establishing the "loans"? Could I tie giving money to signing a document where he gives up any claims? I'd probably need a lawyer for that, right?