Then you can generate a new address for him to avoid using the old one following the method below. And only he knows the private key of the new address.
Suppose Litecoin's elliptic curve base point is G. Then you randomly choose a number a, and calculate aG + P, which is the pub key of the new address, and then take HASH160 of the pub key and you get the new address.
After sending Litecoins to the new address, you tell him a. And then he can calculate the new private key as x+a, where x is the private key of the original address L.
The reason is: since the original private key for P is x, i.e. P = xG, the private key for the new address is then x + a, because (x+a)G = P + aG.
Next, I am going to introduce how to use this trick to create a decentralised Litecoin Blockchain based CoinJoin service for Litecoin.
Besides the litecoin Electrum version of the wallet, is there an HD wallet made for litecoins? Your development team should start making one or at least create a code base for the others to continue and to possibly make one.
It is already known that we should not keep using the same address over and over. So why not have an HD wallet and make it more convenient for the users?
LoafWallet, Jaxx, and soon a few hardware wallets.