Consider making or buying a secure drop box.
5 years ago, I made one from wood which is firmly attached to the wheelie bin storage wall. It has a door at the front and this is secured with a padlock that the Postie finds inside. When he has put the parcel(s) inside, he locks the door with the padlock. Padlock is bright yellow so I can see it as soon as I get home. Capacity is almost wheelie bin size.
OK it handles only one delivery at a time but it's been a most useful bit of kit. Might make another one to take multiple deliveries like this.. [www.ebay.co.uk