Patience, patience, patience....day after day do the same thing over & over & over....

get a tie out stake....a 10-15' cord on it....hook your dog to it.....let him reach the end of the cord....put your hand out like a stop motion (like a police officer stop hand signal) and say whoa... you will have to manually hold the dog there for the first ??? times.....but, eventually he/she will get it....eventually back away little by little to let them know to stay there even when you are going away.
what I do to release them is tap it's head twice (just me) and say ok.....that way they know it's ok to be released from this position...
give them a small treat when done right.