cr. lk > cr. mk/cr. hk is a terrible way to end your block string. cr. lk leaves you at +0 on block, and cr. mk has 8 frames of start up which means you’ll have a pretty big hole that you can be poked out of.
In general, it’s never a good idea to end your strings with cr. lk because it gives you no frame advantage on block and usually pushes you out of jab range, leaving you vulnerable to your opponent’s counterpokes. Note that Rog’s medium/long range pokes all have mediocre start up (7+ frames), so if you end your block string with cr. lk, you’ll have no way of beating out a well timed counterpoke from someone with faster medium range normals.
In case it helps, here are some block string mix-ups I use (aside from the usual tick throw mixups mentioned by Xaaz):
cr. jab (2-3x), walk back -
Jab them out to the tip of their medium poke range, then take a step back while they’re in block stun to make their counter-poke whiff. Ready an fs. hk to punish. This works well against characters who have good medium range pokes, and is also a safe way to gauge how they handle themselves during your block strings at the start of the match.
cr. jab (2-3x), step back, block low -
Use this instead of the first option if you notice that they’re counterpoking your block strings with sweeps, but when you don’t want to risk laying a frame trap for it. You sometimes won’t have enough time to step out of their sweep range to make it whiff, but you can punish certain sweeps (like Ryu’s) on block. Once again, this option is a good way of reading your opponent’s reactions to your block string pressure at the start of a match.
cr. jab (2x-3x), step forward, cr. jab -
Jab them till you can’t reach them with a jab, then step forward into the tip of your jab range and do another crouching jab. Mix this in with your tick throws every now and then if you notice that they’re being extra defensive and are just blocking and late crouch teching. Against certain characters, you can use the delayed cr. jab to start a hit confirm string into cr. hk (cr. lp, fs. lp, cr. hk), or you can take a relatively safe gamble and go directly into cr. hk instead. It should combo on a counter hit, but you can’t hit confirm it.
cr. jab (2x-3x), cr. mp (option select) dash straight -
jab them until they’re outside your cr. mp range, then input cr. mp xx dash straight. If the cr. mp whiffs, you don’t get anything (although note that you risk getting punished for the whiff if they were expecting it). If they were mashing out a normal, the cr. mp will hit their extended hitbox and cancel into dash straight.
cr. jab (1-2x), cr. mk, cr. mk/hk - Jab them outside their jab and short range, then cr. mk > cr. hk. Use this to frame trap your opponent’s medium pokes. This works because cr. mk puts you at +4 on block but has an animation that looks deceptively slow, so some people may get fooled into trying to counterpoke you after blocking it. Note that there are holes in this string, so use it sparingly or not at all against reversal mashers.