Why do you have Paypal connected to a funding source where they could even do this in the first place? The first rule of Paypal is they can't take what isn't there so use funding sources that only have funds when you are making a specific purchase.
So in practice:
Never keep a Paypal balance.
Use one of those disposable credit card services where you can change the amount available on the card or use a debit card connected to an account with $0 in it until your transfer funds in.
Why do you have Paypal connected to a funding source where they could even do this in the first place? The first rule of Paypal is they can't take what isn't there so use funding sources that only have funds when you are making a specific purchase. So in practice: