To block storage location postings the easiest way to achieve this is to use MI01 create inventory document. This is normally used for inventory count. In creating an inventory document (which is used as a counting document) you can select the option to block postings on the location. The storage location block can be undone by deleting or posting the inventory document. In case you do not actually execute a inventory count you wish to delete the document using MI02.
Note: In case you are using batch managed materials you will not be able to use this method, since the inventory document will only block existing material/batch combinations. New batches can still be received.