Stick with it @FrozenShivers, it's all just a learning curve for you to find what works for you. Remember to enjoy the process as well as the 'end' result
Presoaking the wood is always a good idea no matter whether its glued or not as it'll give you a chance to scrub it down and get all the loose bits off once soaked before it goes in
The glueing takes a bit of getting used to but should work well on both dry and wet hardscape, not sure how it didn't work well for you but I usually make sure the hardscape is pretty secure so it can't move and then rip a filter in half, lodge it in and put on the glue, the filter needs to be sodden in glue for it to work so you may need to use more than you think, after in it should be pretty firmly held in place but will still pull apart if not careful and will be solid after about an hour
Oh and just seen @Myrtle post above, I've found the only time it works for me is when it has hard touch points, building up big gaps never sets well for me
Presoaking the wood is always a good idea no matter whether its glued or not as it'll give you a chance to scrub it down and get all the loose bits off once soaked before it goes in
The glueing takes a bit of getting used to but should work well on both dry and wet hardscape, not sure how it didn't work well for you but I usually make sure the hardscape is pretty secure so it can't move and then rip a filter in half, lodge it in and put on the glue, the filter needs to be sodden in glue for it to work so you may need to use more than you think, after in it should be pretty firmly held in place but will still pull apart if not careful and will be solid after about an hour
Oh and just seen @Myrtle post above, I've found the only time it works for me is when it has hard touch points, building up big gaps never sets well for me