How can I properly weld something to a player's character?

I've seen tons of other posts in regards to welding objects to players characters involving WeldConstraints, Welds, or Accessories, but none of them seem to work for me, and when using welds, I run into multiple issues, depending on how I do it. Firstly, if I try to weld something to a character model from the Server, the part does not position properly, and has a terribly noticable offset, usually to do with character movement. If I try and weld things using the Client, it welds properly, but does not replicate to the server, and thus the other players do not see it. How can I properly weld an object to a player's character from the server side, such that the part replicates to the other clients, and doesn't have horrible, nonsense, or weird offsets?