Hi there Julei thanks for posting in the Lucidchart Community. Unfortunately it is currently not possible to lock the size of an object without locking the position at the same time.

However we're always looking for ways to improve Lucidchart and your feedback is the best way for us to do that. Would you mind adding your idea to our feature request form? Ideas submitted to this form are passed on to the product development team for their consideration.

Thanks for your request and I apologize for any inconvenience this causes you.

For anyone else interested in our locking functionality please take a look at the Modify Format and Style Shapes Help Center article for more information.