Maintaining erection during intercourse

Not that it should matter, but I am using the Progasm Aneros product since it works best for me.

if it doesnt feel good then you will have problems getting an erection, other then that I see no reason anal play would stifle an erection. Even with the smallest aneros devices it takes a good 10 minutes before everything is situated and it starts feeling good, so dont rush it, let your body get accommadated to whatever you are putting in there.

Maybe use a cock and ball sling to help keep you up. I know others do on this site.One fellow says it makes his balls slap his wife which she loves.
You can get all different kinds.
This site suggestion has lots of stuff that turns me off completely but there cock slings are very good quality.
http://shop.oxballs.com/COCKSLING-original-by-OXBALLS-CBT-213.htm
Just a though it may not suit you but worth a though at least.

I use a doc johnson medium non skid butt plug for maintaining a hard cock. Progasm pops out during sex

We initially purchased a Helix just to spike my prostate during foreplay and sex. An occasional anal contraction would nudge my erection. It worked but I found that when I climaxred the Helix was sufficiently large so that my 'load' was throttled. Stepping downward to an SGX or Peridise seemed to be a great trade-off.

It may be that the problem is not prostate or perineal stimulation, but rather the fact the device you are using forces the backdoor to open too wide (I know that can cause me to have erection problems.) You might have better luck with a smaller-neck model such as the Eupho (classic or syn) or the new HIH 950 that has been discussed recently in this forum. (I've tried the 950 and I like it -- it's small I find it very effective -- of course, YMMV. I also like its small handle, which doesn't get caught on bedding, etc.) Of course a Peridise is also an option, but it provides no perineal stimulation and it's not primarily designed for prostate stimulation either.