I feel you can practise the R sound alone. More like rrrrrr... That really helped me with that sound. I realised I had trouble saying the word radius. I have noticed so many factors that contribute to my stammering that I don't know which ones are legitimate and which ones are not. But I feel when I try to say radius, the tongue goes to the upper teeth and as I am beginning to say it, it slips a bit and my brain notices it. Normally, if we stumble on a word, our instinct is to say the word again. So, I feel my brain notices the slip and knows that it will be better if I start over even though I consciously feel I can still say it. I realized that the slip happened because of my existing stammering issues. We constantly doubt ourselves and we aren't coherent in our speech. If we doubt and pause our mind even for a second, the tongue is going to say the word out of habit but we aren't conscious of it and we think it slipped because as soon as we are conscious of it...it won't go all the way and it stops. Mind you...the slip is only a little bit and the issue is that our brain notices it. I've practised saying rrrrrr continuously and it has really helped me in getting the habit of saying the r sound and I don't seem to have any issue now. Because of my stammering, I have been so conscious of every word that tougher sounds have been hard these days. Never had an issue with them before. Especially the word shrink. When I was younger, I used to just say it but now I'm conscious of each and every sound that there is no smooth flow. The shri part will be proper only if we say it continuously. I had to practise saying it continuously for quite some time in order to get it. So, I have been practising speaking like a child. Normally, smoothly and without being conscious of the words. These days...texting a lot makes us associate sounds with the letters of the alphabet. We should try to not do that and purely focus on the words coming out of our mouth. We should try saying words as a whole.