In My Opinion

Most Speechies will agree that R is one of the hardest phonemes to correct.  R is especially difficult, because there is a variety of R phonemes (prevocalic/intitial R and several vocalic R's.  To complicate this further, there are 2 ways to produce the R sound.  With myself, I have observed that I use both methods for R production depending on the phonemes surrounding R.  As Speechies, we know that sometimes we have to use some "unconventional" or rather unusual methods to stimulate resistant phoneme production.

When in I attended USD, Dr. Hansen demonstrate a floor exercise to stimulate the prevocalic R.  First, have the student lay flat on their back with their chin pointed directly at the ceiling.  (Gravity helps to pull the tongue back into position.)  Second, have the student make Grizzly Growls .... Grrrrr.  Then move into R growls ... Rrrrr.  Third, have the student R growl with a vowel (long & short).  Fourth, have the student R growl CVC phoneme words ie. ripe, reach, rap, etc.  As the student becomes more successful with these, have them lose some of the growl in the production of R.

I also watched a Youtube video on R production that I found quite helpful in the production of EAR, AIR and IRE.  https://www.youtube.com/watch?v=DU72wUNozVE