Looking for exercises to deal with fossilised pronunciation mistakes in adult learners

Their English learning journey looks something like this. They had English at school but as a second foreign language and not for long, maybe three years. Then they didn't use it for ages. Then they were forced to use it e.g. in a work setting but never had the time to reflect on how to use it. And now they come to me to learn it "properly". 😉 I guess in some cases the instructions they got in school weren't that great to begin with. And then there are interferences from their L1 and other languages they learned.

I'm aware of minimal pairs. They are great for practising vowels for example. But only useful at a certain stage. Another exercise I do with intermediate learners, when I notice they struggle with pronunciation, focuses on word and sentence stress. But none of these are helpful when a learner can't even hear the difference between s, z, ʃ, and θ or between a monophthong and a diphthong. A really common mistake seems to be to pronounce silent letters, which I actually expect to be difficult and know how to deal with, but also to add a sound at the end of the word that isn't even there in writing.

And, yeah, I'm already telling my students to listen to English a lot, give them links to podcasts at their level, and we do plenty of listening and speaking exercises in class. I just hope I could expand my repertoire a bit by learning from your experiences.

Thanks in advance!