There are two issues here:
- A final 'r' is not usually sounded. There are exceptions. See related threads.
- Most native speakers, in words ending with a stop consonant (/p t k b d g/}, form the closure but don't release it. This doesn't mean there's no closure - which is what many students do (with /t k d/ and /g/, there are very few visual cues, but that doesn't mean native-speakers don't do it ) . The situation is further confused sometimes, informally, by the Glottal stop - Wikipedia, the free encyclopedia - which reinforces (and sometimes replaces the closure) - but you probably don't need to bother with this.
- For Teachers