We are on holiday at the moment and when we start the day my husband inserts a long silicone butt plug and keeps this in until we play…
He uses lots of lube and hourly takes out - re lubes and puts back- but I notice it leaks lube and leaves a clear water mark on his trousers
He wears wet look knickers but it just leaks through
just wondering what others use - ??? Please help 
I could only suggest some sort of absorbent pad… can i ask why having the plug in is such a necessary thing…does it make things that much better when you play ?
How thick is the neck of the toy? If the neck is too slim, the sphincter can’t always close enough to make a tight seal around it, which will increase the chance of leaking. I’m not talking about using anything big, but a couple of millimetres can make a difference.
My other thought is that he could be over lubing. When he removes to top up, is the toy coming out dry? Does he top up hourly out of habit or is that when it’s becomes uncomfortable? If there is still lube remaining, he could cut back the amount he uses or the frequency he is topping up.
Alternatively, use an oil based lube. It is more slippery and longer lasting than water based so he can use less, and top up less frequently and it’s fine with silicone toys.
Otherwise, i agree with @Iwill and think a panty liner would be the best bet unless you wanted to find him some suitable period underwear. I haven’t seen wet look ones, but there are some prettier options out there
Being as I do the laundry , my first thought was water based lube does not stain generally , silicone may . I have very slender necks on my butt plugs , very little leakage . Keep in mind water based lube is absorbed , so re lube will be needed for extended use . the non water based should not have to be applied often . The other thing that comes to mind is how many people on the forums talk about how far they can stretch their butts . If your husband does that , you might suggest taking a break from giant butt plugs and see if problem persists . The body can recover from stretching unless it does not have a break from Godzilla size butt toys .
My first thought would be to use a panty liner. Lube gets everywhere, especially if its got any amount of silicone in it.
And be just a little wary of using silicone based in your butt. It IS considered very body safe to use but silicone is essentially a ‘water proofing’ that blocks your bodies ability to absorb fluids and requires a soap to be removed fully in any good amount of time. Anything that prevents your bowels ability to absorb water needs some consideration.
There are also some older lubes on the market that contain preservatives and anti fungal and microbial agents that are known to cause irritation and worse. Always check the ingredients. If its not silicone it WILL get absorbed into your body, your blood stream and every where else, and that might not be something you want.
@Iwill - he feels good wearing a plug - when home it’s then easy for pegging as the anus us already stretched
Oh dear Lordy! Hope it wasn’t noticeable when you both was out 
The simplest solution I can think of other than getting him to wear a woman’s pantie towel, is to get a few sheets of lichen roll and tactfully place it in his pants so it covers the bum and will absorb any leakage residue while adding a barrier from it going on his trousers and showing 
@batjamboree …I knew he enjoyed pegging , but didnt realise it was his priority. It does appear he goes to quite a length to facilitate the sexual act.
Im not into pegging ( it scares me to be quite honest), but gentle stimulation of the entrance is enjoyable.